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Review
Non-conventional water resources and opportunities forwater augmentation to achieve food security inwater scarce countries
M. Qadir a,*, B.R. Sharma b, A. Bruggeman a, R. Choukr-Allah c, F. Karajeh d
a International Center for Agricultural Research in the Dry Areas (ICARDA), P.O. Box 5466, Aleppo, Syriab International Water Management Institute (IWMI), Asia Regional Office, CG Block, NASC Complex, DPS Marg,
Pusa Campus, New Delhi 110 012, IndiacSalinity and Plant Nutrition Laboratory, Institut Agronomique et Veterinaire Hassan II, B.P. 773 Agadir, MoroccodDepartment of Water Resources, Recycling and Desalination Branch, Office of Water Use Efficiency,
901 P Street, P.O. Box 942836, Sacramento, CA 94236-0001, USA
a r t i c l e i n f o
Article history:
Accepted 21 March 2006
Published on line 24 May 2006
Keywords:
Water scarcity
Seawater desalination
Rainwater harvesting
Marginal-quality water
Wastewater
Saline–sodic water
Virtual water
Water transportation
a b s t r a c t
Given current demographic trends and future growth projections, as much as 60% of the
global population may suffer water scarcity by the year 2025. The water-use efficiency
techniques used with conventional resources have been improved. However, water-scarce
countries will have to rely more on the use of non-conventional water resources to partly
alleviate water scarcity. Non-conventional water resources are either generated as a
product of specialized processes such as desalination or need suitable pre-use treatment
and/or appropriate soil–water–crop management strategies when used for irrigation. In
water-scarce environments, such water resources are accessed through the desalination
of seawater and highly brackish groundwater, the harvesting of rainwater, and the use of
marginal-quality water resources for irrigation. The marginal-quality waters used for
irrigation consist of wastewater, agricultural drainage water, and groundwater contain-
ing different types of salts. In many developing countries, a major part of the wastewater
generated by domestic, commercial, and industrial sectors is used for crop production in
an untreated or partly treated form. The protection of public health and the environment
are the main concerns associated with uncontrolled wastewater irrigation. The use of
saline and/or sodic drainage water and groundwater for agriculture is expected to
increase. This warrants modifications in the existing soil, irrigation, and crop manage-
ment practices used, in order to cope with the increases in salinity and sodicity that
will occur.
It is evident that water-scarce countries are not able to meet their food requirements
using the conventional and non-conventional water resources available within their bound-
aries. Another option that may help to achieve food security in these countries is the
‘physical’ transportation of water and food items across basins, countries, and regions.
Long-distance movement of surface freshwater or groundwater and transporting the water
nes
int
inland via large pipeli
transportation. Most
* Corresponding author. Tel.: +963 21 2213433; fax: +963 21 2213490.E-mail address: m.qadir@cgiar.org (M. Qadir).
0378-3774/$ – see front matter # 2006 Elsevier B.V. All rights reservedoi:10.1016/j.agwat.2006.03.018
or across the sea in extremely large bags are examples of ‘physical’
erregional water transportation projects are still in their infancy,
d.
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 2 3
though the trade of food items between countries has been going on since international trade
began. Although food is imported in the international food trade, the water used to produce
the food that is imported into water-scarce countries is equivalent to large water savings for
those countries: without the imports, almost the same amount of water would be needed to
produce that food domestically. The term ‘virtual water’ has been used to illustrate the
important role that water plays in the trade in food between countries with a water surplus
and those with a water deficit, which must rely in part on importing food to ensure food
security. Because the major food-exporting countries subsidize their agricultural production
systems, food-importing countries need to consider both the policies and political situations of
food-exporting countries, while simultaneously using food trade as a strategic instrument to
overcome water scarcity and food deficits. This paper reviews the literature and issues
associated with the use of non-conventional water resources and opportunities for achieving
food security in water-scarce countries.
# 2006 Elsevier B.V. All rights reserved.
Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Non-conventional water resources in water-scarce countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Desalinated seawater and highly brackish groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Rainfall-runoff water captured by water harvesting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.3. Marginal-quality water resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.1. Wastewater from domestic, municipal, and industrial activities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3.2. Agricultural drainage water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.3. Saline and/or sodic groundwater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
3. Opportunities contributing to food security in water-scarce countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.1. Physical transportation of freshwater. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2. Food imports and the ‘virtual water’ nexus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
4. Future perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
Looking at the natural global water cycle that yields an annual
renewable water supply of about 7000 m3 per capita (Shiklo-
manov, 2000), it is evident that there is enough freshwater
available every year to fulfill the needs of the present population
of this planet. However, in certain regions and countries the
annual renewable supply of water is less than 500 m3 per capita.
In addition, the availability of water varies greatly over time in
these areas, which results in extreme events. Floods and
droughts, for example,occur frequently, sometimes inthe same
area or neighboring regions. What this contrast illustrates is
that most of the freshwater available is concentrated in specific
regions, while other areas are water-deficient (Pimentel et al.,
1999; Rijsberman, 2006). Because freshwater resources and
population densities are unevenly distributed worldwide, water
demands already exceed supplies in regions that contain more
than 40% of the world’s population (Bennett, 2000).
Of particular concern is the situation in the Middle East and
North Africa (MENA), which ran out of renewable freshwater
decades ago, in the sense that the region is unable to meet its
food requirements using the available water resources. This
region is the driest on earth, containing only 1% of the world’s
freshwater resources. However, several countries in other
regions have also recently encountered a water deficit (Allan,
2001). And, datasets and maps published in recent years show
that more and more countries will become water-stressed
because of increased water scarcity (Seckler et al., 1998; FAO,
2003; Table 1). Bearing in mind the recent trends seen in water
withdrawal under present practices and policies, future
projections suggest that by the year 2025 about 60% of the
world’s population will have to cope with a lack of water
(Cosgrove and Rijsberman, 2000).
In order to achieve adequate living standards equivalent to
those seen in western and industrialized countries, an annual
renewable water supply of at least 2000 m3 per capita is
required (Postel, 1993). By the same token, a country with
annual renewable water supply of 1000–2000 m3 per capita
may suffer occasional or local water shortages (Bouwer, 2002).
According to Falkenmark and Lindh (1993), an annual fresh-
water supply of 1000 m3 per capita is the critical value.
Countries with less than this will suffer serious water
shortages that could impact on economic development, and
human health and well-being. Generally known as the
‘Falkenmark Indicator’, this is the most widely used water
scarcity index because it is easy to apply. It is based on an
approximate minimum level of water required per capita to
maintain an adequate quality of life in a moderately developed
country. When annual renewable water supplies fall below
500 m3 per capita, a country is likely to experience ‘absolute
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 24
Table 1 – Estimates and projections of populations and ofrenewable water resources (RWR) per capita in 2005 and2030 for countriesa that are expected to fall below thewater scarcity level (1000 m3 capitaS1 yrS1) in the year2030
Country Population(�103)
RWR(m3 capita�1
yr�1)b
2005 2030c 2005 2030d
Kuwait 2671 4198 7 5
United Arab Emirates 3106 4056 48 37
Saudi Arabia 25626 43193 94 56
Libya 5768 8123 104 74
Singapore 4372 4934 137 122
Jordan 5750 8643 157 104
Yemen 21480 50584 191 81
Israel 6685 8970 254 190
Oman 3020 5223 331 191
Algeria 32877 44120 435 324
Tunisia 10042 12351 458 372
Burundi 7319 13652 492 264
Rwanda 8607 13453 604 387
Egypt 74878 109111 779 534
Burkina Faso 13798 27910 906 448
Morocco 31564 42505 919 682
Kenya 32849 41141 919 734
Lebanon 3761 4692 1170 938
Somalia 10742 24407 1257 553
Malawi 12572 19834 1376 872
Pakistan 161151 271600 1382 820
Syria 18650 28750 1410 915
Eritrea 4456 7942 1414 793
Ethiopia 74189 127220 1483 865
Based on water resources data from FAO (2005) and population
data from WRI (2005).a Countries with limited area, population or data (e.g., Bahamas,
Qatar, Malta) were not included.b RWR include internal renewable water resources plus or minus
the flows of surface water and groundwater entering or leaving the
country, respectively.c UN medium variant population projections for the year 2030.d Based on the assumption that the RWR in the countries in 2030
will remain the same as in 2005.
water scarcity’. Besides the ‘Falkenmark Indicator’, other
water scarcity indicators exist that provide a greater insight
into the different aspects of water scarcity. However, these
indicators are not widely applied because: (1) they are more
complex, (2) the data necessary to apply them are lacking, and
(3) their definitions are not intuitive (Rijsberman, 2006).
Agriculture is the largest single user of water, with about 75%
of the world’s freshwater being currently used for irrigation. In
some countries, irrigation accounts for as much as 90% of the
total amount of water available (FAO, 2003, 2005). Given that
water productivity in agriculture continues to be low and that
improvements are only being made very slowly, and that
freshwater has always been an integral component of food
production, it is obvious that huge amounts of water will be
requiredtoproduce enoughfoodfor the futurepopulationof the
world. In addition, urbanization and increasing populations in
water-deficient countries increase the demand for freshwater.
This results in competition among different water-use sectors
and, often, in less freshwater being allocated to agriculture.
Such priority-setting results from the fact that, at all times,
public needs and people’s health have to be protected through
the use of the best quality water available. The phenomenon of
agriculture having to yield part of its share of the freshwater
available is expected to intensify in those less-developed, arid
and semi-arid countries and regions that are already suffering
water, food, sanitation, and health problems.
As the pressure placed on freshwater resources in water-
deficient regions increases, so will the need to conserve and use
conventional water resources more efficiently, because future
increases in agricultural production will have to rely heavily on
existing water resources (Oweis et al., 2000; Wallace, 2000;
Hatfield et al., 2001; Kijne et al., 2003). Such conventional
resources consist of the water available from rainfall and
snowmelt, which is used on site or taken from rivers, streams,
lakes, reservoirs, and aquifers. These resources are renewable
through the natural processes of the hydrological cycle.
In addition to conventional resources, non-conventional
water sources offer complementary supplies that can be used to
partially alleviate water scarcity in regions where renewable
water resources are extremely scarce. Such water resources are
harnessed for agricultural and other uses through specialized
processes such as desalination of seawater and highly brackish
water; harvest of rainwater; collection, treatment, and use of
wastewater; capture and reuse of agricultural drainage water;
extraction of groundwater containing a variety of salts.
Appropriate strategies for managing soil, water and crops
may also be needed when theseresources are used for irrigation
(Mohsen and Al-Jayyousi, 1999; Voutchkov, 2004; Oweis et al.,
2004; Qadir and Oster, 2004).
The ‘physical’ transportation of water and food items
across basins, countries, and regions is another option that
could help countries in the dry regions to achieve food
security. Tapping freshwater from surface water resources or
aquifers and moving the water via large pipelines or by sea in
huge bags, are examples of ‘physical’ transportation, a
definition which does not include contiguous gravity-flow
movement systems such as rivers and canals (Mohsen and Al-
Jayyousi, 1999; Ariyoruk, 2003). Most water transportation
projects are still in their infancy. However, food has been
traded internationally as long as there have been wagons,
railroads, ships, and now airplanes. Although food, not water,
is imported in the international food trade, the water used to
produce the food that is imported into water-scarce countries
is equivalent to large water savings for those countries:
without the imports, almost the same amount of water would
be needed to produce that food domestically. The term ‘virtual
water’ has been used to illustrate the importance of water in
the trade of food between water-surplus and water-deficit
countries (Allan, 1996, 2003). This paper reviews the literature
and the issues concerned with the use of non-conventional
water resources and those other opportunities that could be
used to increase food security in water-scarce countries.
2. Non-conventional water resources inwater-scarce countries
Non-conventional water resources have the potential to
augment water supplies and narrow the gap between fresh-
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 2 5
water availability and demand in water-scarce countries and
regions. These water resources are considered in turn below.
2.1. Desalinated seawater and highly brackishgroundwater
Seawater contains high concentrations of salts. It has
electrical conductivity (EC) levels of around 55 dS m�1 (total
dissolved solids �35,000 mg L�1) and sodium (Na+) concentra-
tion of more than 450 mmol L�1 (�10,400 mg L�1). Without
treatment to reduce its salt content, humans or animals
cannot use seawater directly for consumption, as this would
severely affect their health; nor can untreated seawater be
used to produce crops (Qadir et al., 2003). The same is true of
highly brackish groundwater containing elevated levels of
various types of salts.
Desalination, a process that converts seawater or highly
brackish groundwater into good-quality freshwater, has been
practiced for over 50 years. The scarcity of freshwater has
provided a driving force for the use of this approach in arid and
semi-arid regions and in countries bordering seas or salt lakes.
The largest producers of freshwater from seawater are the
Middle Eastern countries, including Saudi Arabia (which
produces one-tenth of world’s desalinated water), the United
Arab Emirates, Kuwait, Bahrain, Qatar, and Oman. However,
several other countries have a compelling need to desalinate
seawater and highly brackish groundwater to produce fresh-
water. These countries are not all located in the arid and semi-
arid areas: some simply have dense population concentrations
and high levels of industry and tourism, resulting in local
drinking water resources being either inadequate or becoming
unfit for consumption. Currently, desalination plants operate
in more than 120 countries worldwide (Voutchkov, 2004).
Estimates show that each day desalination plants throughout
the world produce about 30 � 106 m3 of freshwater: about
20 � 106 m3 from seawater and the remainder from highly
brackish groundwater (Pearce, 2004). This suggests that the
total amount of freshwater produced each year from desali-
nation is around 11 � 109 m3.
Since the advent of desalination, several processes have
been used to desalinate seawater or highly brackish ground-
water. Some have been disregarded because they were not
economically viable. Among the main desalination techni-
ques, distillation is the oldest form of seawater treatment, and
is a process that has been used in many parts of the world.
Desalination using distillation can be accomplished in several
different ways (Semiat, 2000). In general, the process uses heat
energy to evaporate water and thus separate it from salts and
impurities. The evaporated water is then captured and
condensed as freshwater. The process therefore recreates
the cycle of evaporation and condensation of water that
occurs naturally. However, distillation is an energy-intensive
process. Initially, therefore, distillation plants were con-
structed in areas where the energy costs were very low (such
as the oil-rich Middle East) or near to processing plants which
produced waste heat (Haddad and Mizyed, 2004).
In order to reduce energy costs, the seawater reverse
osmosis process was developed in the 1970s. This is a more
energy-efficient process, which makes use of tightly bound
semipermeable membranes, through which seawater is
forced at very high pressures. Only the water molecules are
able to pass through these membranes, as they are smaller
than almost all the impurities (including salts) contained in
seawater. The separated impurities and some residual water
are then discharged as brine, usually into the ocean. Advances
in membrane technologies have also led to the emergence of
membrane configurations with different performance para-
meters. This method of desalination became popular during
the 1990s, as it has a lower operating cost than thermal
desalination processes. Since then, the construction of new
reverse osmosis plants has accelerated significantly. Interest-
ingly, most of the large desalination plants constructed during
the last 10 years, or currently undergoing construction, are
delivered under public–private partnership arrangements
using the build–own–operate–transfer method of project
implementation. In addition, the trend has been towards
building fewer seawater desalination plants but ensuring that
those built have a large capacity, rather than building a large
number of smaller facilities with less capacity. This is a result
of the benefits offered by larger capacities and centralization
(Voutchkov, 2004).
A comparison of desalination techniques reveals that
distillation plants have an advantage in that they produce
high-quality water that usually contains in the range of
5–50 mg L�1 (mg L�1 = parts per million, ppm) of dissolved
solids in total, while reverse osmosis plants produce water
that contains between 250 and 500 mg L�1 of dissolved solids
in total (Mohsen and Al-Jayyousi, 1999; Semiat, 2000). Another
advantage of distillation plants is the fact that one does not
have to shut down a portion of their operations to clean them
or to replace equipment, something which often has to be
done in reverse osmosis plants. In addition, the pre-treatment
requirements of reverse osmosis plants are greater, because
coagulants are needed to settle out particles in the water
before it passes through the membranes and to remove
chemical constituents that could precipitate in the mem-
branes.
The reverse osmosis plants do have advantages over
distillation plants. These include the fact that feed water for
reverse osmosis plants generally does not have to be heated,
so the thermal impacts of discharges are lower. In addition,
reverse osmosis plants have fewer problems with corrosion
and usually have lower energy requirements than distillation
plants. They also tend to have higher recovery rates, which
can be as high as 45% in the case of seawater. Reverse osmosis
process can also remove unwanted contaminants such as
pesticides and bacteria. In the case of simple distillation,
chemical contaminants with boiling points below that of
water are condensed along with the water. Finally, reverse
osmosis plants take up less surface area than distillation
plants for the same amount of freshwater produced.
The cost of energy is the major cost involved in producing
freshwater through desalination using the reverse osmosis
process (Fig. 1). The overall cost of seawater desalination, once
quite high, has dropped dramatically over the years. For
example, the costs of desalination in late 1970s were around
US$ 5.5 m�3, but now vary between US$ 0.5 and 0.6 m�3,
depending on the site and size of the treatment plant.
However, the rate of incremental cost reductions has declined
over time (Ariyoruk, 2003; Pearce, 2004; Haddad and Mizyed,
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 26
Fig. 1 – Typical seawater desalination costs through
reverse osmosis in terms of percentage of the total cost
(Semiat, 2000).
2004). The cost of desalinated water is not expected to
decrease by an order of magnitude any time soon. It is
anticipated, however, that this cost will go down by
approximately 20% in the next 5 years, and that it will
decrease by close to 50% by the year 2020. This is because the
current energy use of reverse osmosis desalination systems is
between 10 and 20 kJ m�3, whereas with the newest energy-
recovery technology, which allows the reuse of a proportion of
the energy used for desalination, energy use could be reduced
to 7.2 kJ m�3. However, this value is still 44% greater than the
theoretical minimum amount of energy needed for seawater
desalination (Voutchkov, personal communication, 2005).
Nuclear and solar energy could also be used to provide the
heat needed to desalinate seawater, providing another
opportunity for the desalination of seawater on a large scale.
By the same token, wind energy is an option that could be used
in conjunction with small-scale desalination units.
Although the existing costs of desalination and desalinated
water distribution are affordable in many developed and oil-
rich countries, desalinated water is still an expensive resource
in developing countries. Bearing in mind the costs of other
conventional and non-conventional water resources, which
could be used for agriculture, the use of desalinated water for
traditional agricultural production systems remains an
expensive option, although desalinated water is being used
on a small scale for high-tech and high-value agriculture in
areas such as southeastern Spain. The costs of investments
and operation are shared equally between farmers and the
government to overcome the recurrent droughts this region of
Spain experiences. In the 1990s, the estimated financial losses
in Spain due to drought were around US$ 120 million. Since
1994, more than 90 reverse osmosis plants have been installed
in this part of Spain with a total daily desalination capacity of
0.15 � 106 m3 and an annual production rate of 55 � 106 m3 of
desalinated water (Latorre, 2002).
Desalination does have environmental implications,
because the effluents produced by desalination plants contain
highly concentrated water. In the case of seawater desalina-
tion, the brine effluent generated has a concentration of salts
close to twice that of the original seawater. The concentrate
also contains the chemicals used during the pre-treatment of
the feed water. When those concentrates are produced inland,
as occurs in the case of the desalination of highly brackish
groundwater, disposal in unlined ponds may cause the brine
to seep to the aquifer, thereby increasing groundwater salinity
(Semiat, 2000). For desalination of seawater, the solutions are
generally purged into the open sea. This warrants study of the
best options for brine disposal systems, in order to maximize
brine dilution. In addition, the possible impacts of brine on a
variety of marine habitats require regular monitoring. Studies
are underway in some countries to develop environmentally
acceptable and efficient brine disposal systems (Latorre, 2002).
It is important that adequate regulations, policies, and
practices are in place to prevent desalination having a
negative impact on adjacent areas and the wider environment.
2.2. Rainfall-runoff water captured by water harvesting
In arid and semi-arid regions, rainfall is limited and subject to
high intra- and inter-seasonal variability. In addition, poor
vegetative cover and shallow and crusting soils result in much
of the rainwater that does fall being lost through surface
runoff and evaporation. These factors provide a strong
impetus for strategies that make best use of the rainfall and
runoff water. Water harvesting is often practiced in areas
where the rain itself is not sufficient for crop production.
Water harvesting for agriculture involves collecting the
rainwater that runs off a catchment area in a reservoir or in
the root zone of a cultivated area, which is usually smaller
than the size of the catchment area (Boers and Ben-Asher,
1982). Owing to the intermittent nature of runoff events, it is
necessary to store the maximum amount of rainwater during
the rainy season so that it can be used later (Oweis et al., 1999).
Water harvesting techniques can be classified in several
ways. In general, water harvesting may be broadly classified
into: (1) macro-catchment and floodwater harvesting and
diversion methods, and (2) micro-catchments methods, where
the catchment area and the cropped area are distinct but
adjacent to each other. Boers and Ben-Asher (1982) define
micro-catchment systems as systems where the catchment
area is less than 100 m in length.
Macro-catchment techniques capture runoff water from
hillsides or small arid watersheds. Soil bunds or small dikes
can be placed on the gently sloping land below hillsides to
harvest runoff water that crops or trees can use. These
systems often have small spillways, to divert excess water
from one field to the next. Water is also sometimes captured
from small arid watersheds in wadi-beds; in these dikes are
used to capture both water and sediment, resulting in deep
fertile soils. The runoff water can also be diverted from the
wadi and used on adjacent cropland. Small storage and
groundwater recharge dams and ponds, which can provide
water for supplemental irrigation of rainfed crops, are also
considered to be macro-catchment water harvesting sys-
tems.
Different forms of micro-catchments have been used in
low rainfall regions. Contour bunds consist of earth, stone or
trash embankments placed along the contours of a sloping
field or hillside, in order to trap rainwater behind them and
allow greater infiltration. Semicircular, trapezoidal or ‘V’-
shaped bunds are generally placed in a staggered formation,
allowing water to collect in the area behind the bunds. Excess
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 2 7
water is displaced around the edges of the bund when the
‘hoop’ area is filled with water. These systems are most
commonly used for growing fruit trees or shrubs.
Another type of water harvesting system involving micro-
catchments is the meskat-type system. In this system, instead
of alternating catchment and cultivated areas, the field is
divided into a distinct catchment area that is located directly
above the cropped area. The catchment area is often stripped
of vegetation to increase runoff. The cultivated area is
surrounded by a ‘U’-shaped bund in order to hold the runoff.
In Tunisia, tree species such as olive (Olea europaea L.) are
grown in these systems (Oweis et al., 2001, 2004). A similar
system, called Khushkaba, is used in Balochistan, Pakistan, for
growing field crops (Oweis et al., 2001).
Rainwater can also be harvested from rooftops or from
sloping, rocky or crusting lands and collected in under- or
above-ground cisterns. These types of systems are often used
for domestic or livestock needs or for the irrigation of home
gardens or small plots of high-value crops. This may not have
a large impact of the nation’s food security but can have an
important impact on the livelihood of rural families in water
scarce areas.
Another form of water harvesting in dry areas is known as
‘fog-harvesting’ in which water from condensation is collected
on a wire screen or net. The wire net is connected to a
drainpipe, which empties into a bucket, and can be placed on
house roofs. The collected water can serve as a source of water
for human consumption in areas where running water is not
available for part of the year and fogs occur frequently.
Guidelines for implementing micro-catchment systems are
available in the relevant literature (Boers and Ben-Asher, 1982;
Critchley and Siegert, 1991; Oweis et al., 2001). In addition to
the characteristics of the rainfall, several landscape char-
acteristics also influence the efficiency of different rainwater
harvesting techniques in the same area. The following on-site
factors influence the usefulness of rainwater harvesting
systems:
1. T
Td
Y
1
1
1
M
Ma
b
he slope of the landscape, which allows runoff water to
flow down where it can be intercepted and collected (Oweis
et al., 1999).
2. T
he texture and structure of the soil. For example, thesurface of soils dominated by a sand fraction in the top layer
and a clayey subsurface can erode at an accelerated rate
able 2 – Shrub survival rate (%) within semicircular micro-catchimensions in the Mehasseh steppe of Syria that receives 120 m
ear Rainfall (mm) Survival without WHa
997–1998 174 20
998–1999 36 7
999–2000 42 2
ean 83 10
odified from Oweis and Hachum (2003).
WH = water harvesting.
Diameter of the semicircular micro-catchment water harvesting structure
when overgrazing, or some other mechanism, removes the
vegetation covering it. This can result in the clayey
subsurface, which has crusting properties and low infiltra-
tion rates, being exposed. These unproductive areas can be
used for water harvesting by inducing runoff to flow to the
cultivated area below (Tabor, 1995). When a hard layer has
not formed on the catchment area, the soil’s surface can be
treated with water-repellent materials that fill the soil pores
and help to reduce infiltration rates, so promoting runoff
(Oweis et al., 1999). However, the present costs of these
materials limit their widespread use.
3. S
oil nutrient availability status, which is essential inenhancing the effects of water harvesting by increasing
crop yields. Increasing the nutrient availability status of the
soil can promote root development, which increases crop
water uptake and biomass production (Rockstrom and
Falkenmark, 2000). Thus the regular application of animal
manure is also important, as manure increases nutrient
levels and improves the physical condition of cultivated soil
(Tabor, 1995).
4. S
oil depth of the cultivated area. The soil must be deepenough, and of a medium-texture, to induce rainfall
infiltration and retention. Deep soils retain greater amounts
of water for plant growth.
Micro-catchment rainwater harvesting systems are advan-
tageous because they are simple to design and cheap to install;
they are therefore easy to reproduce. They can also be adapted
for use on almost any kind of slope, including slight slopes on
almost level plains. Local people can easily be trained to im-
plement such technologies. With little conveyance losses, t-
hese systems provide higher levels of runoff efficiency than
macro-catchment water harvesting systems.
There are several recent success stories relating to micro-
catchment rainwater harvesting. For instance, in the Mehasseh
steppe in Syria, where annual rainfall is 120 mm, the survival
rate of rain-fed shrubs improved to as much as 93% through the
use of micro-catchments in the form of semicircular bunds
(Table 2). By the same token, in the Muwaqar area of Jordan
(annual rainfall 125 mm) almond trees have been grown using
micro-catchments for over 15 years without irrigation, despite
some years of drought during which rainfall dropped as low as
60 mm (Oweis and Hachum, 2003).
One disadvantage of water harvesting systems is that they
depend on limited and uncertain rainfall. Other disadvantages
ment water harvesting structures with differentm annual rainfall on average
Survival with micro-catchment WH
2 m diameterb 4 m diameter 6 m diameter
96 98 97
92 95 93
92 93 89
93 95 93
.
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 28
Table 3 – Volume of wastewater generated annually insome countries of Central and West Asia and NorthAfrica
Country Reportingyear
Wastewatervolume
(�106 m3 yr�1)
Algeria 2004 600
Bahrain 1990 45
Egypt 1998 10012
Iran 2001 3075
Jordan 2004 76
Kuwait 1994 119
Kyrgyzstan 1995 380
Lebanon 1990 165
Libya 1999 546
Morocco 2002 650
Oman 2000 78
Saudi Arabia 2000 730
Syria 2002 825
Tunisia 2001 240
Turkey 1995 2400
United Arab Emirates 2000 881
Uzbekistan 2004 170
Yemen 2000 74
Except for Algeria, Jordan and Uzbekistan; data derived from the
wastewater databases of the Food and Agriculture Organization,
available at http://www.fao.org/landandwater/aglw/waterquality/
waterusedb.jsp.
are that: (1) the catchment area is most efficient when kept
free from vegetation, which may require high labor inputs; (2)
the system may be damaged during heavy rainstorms and
need regular maintenance; (3) the catchment uses land which
could otherwise be used to grow crops, if sufficient water is
available, except in the case of steep slopes; (4) the systems
allow only low crop densities and low yields in comparison
with conventional irrigation systems (Prinz, 1996).
Various rainwater-harvesting techniques have a long
history of use, and have resulted in increases in crop yields
and water-use efficiency in different parts of the world
(Agarwal and Narain, 2003; Pandey et al., 2003; Oweis et al.,
2004). Many plant species with low to medium water
requirements have been successfully grown using different
water harvesting techniques. Owing to population pressure in
water scarce countries, interest in the use of water harvesting
and conservation strategies has been growing. For example,
estimates show that the quantities of water harvested in
Jordan have reached 6 � 106 m3 yr�1 (Jaber and Mohsen, 2001).
Although the exact amount is difficult to estimate, Oweis and
Hachum (2003) have revealed that 30–50% of the rain that falls
in the drier regions could be utilized if appropriate water
harvesting techniques were practiced. Utilizing rainwater in
this way has the potential to result in a several-fold increase in
rainwater-use efficiency in water-scarce environments.
2.3. Marginal-quality water resources
Marginal-quality waters consist of: (1) wastewater generated
by domestic, commercial and industrial uses; (2) drainage
water generated by irrigated agriculture and surface runoff
that has passed through the soil profile and entered the
drainage system; (3) groundwater from different sources, such
as underlying saline formations, seawater intrusion in coastal
areas, recharge of agricultural drainage, storm water runoff
from urban areas, and/or infiltration from wastewater-
irrigated areas. Marginal-quality waters contain one or more
impurities at levels higher than in freshwater, including salts,
metals, metalloids, residual drugs, organic compounds,
endocrine-disrupting compounds, and the active residues of
personal care products and/or pathogens. These constituents
may have undesirable effects on soils, crops, water bodies, or
human and animal health.
2.3.1. Wastewater from domestic, municipal, andindustrial activitiesPopulation growth coupled with the provision of goods and
services that allow higher living standards have increased the
demand for good-quality water to provide for the needs of the
domestic, municipal, and industrial sectors in water-scarce
countries. Consequently, greater amounts of wastewater are
being generated. After treatment, and in conjunction with
suitable management practices, this could be reused for a
variety of purposes. Urban wastewater consist of a combina-
tion of some or all of the domestic effluent produced (black
water and grey water), water produced by commercial
establishments and institutions (including hospitals), indus-
trial effluent and storm water which has not infiltrated the
soil, as well as other forms of urban runoff (Van der Hoek,
2004).
Estimates of the extent to which wastewater is used for
agriculture worldwide reveal that at least 2 � 106 ha are
irrigated with treated, diluted, partly treated or untreated
wastewater (Jimenez and Asano, 2004). The use of untreated
wastewater is intense in areas where there is no or little access
to other sources of irrigation water. Few databases are available
that describe the extent to which wastewater is used for
agriculture at the nationalor regional levels (Minhas and Samra,
2003; Van der Hoek, 2004). Owing to the variable quantities of
water available for human consumption in water-scarce
countries, estimates of the per capita generation of wastewater
vary, ranging from 30 to 90 m3 yr�1. The volumes of wastewater
generated insomecountries ofCentral and WestAsiaand North
Africa (CWANA) are presented in Table 3. A significant part of
the wastewater generated in these countries is used to
supplement the freshwater needs of a variety of crops.
The rate at which populations are increasing means that
wastewater treatment and its sustainable use is an issue that
requires more attention and investment. Most developing
countries have not been able to build wastewater treatment
plants on a large enough scale and, in many cases, they were
unable to develop sewer systems fast enough to meet the
needs of their growing urban populations. As a result, in
several countries, particularly in Sub-Saharan Africa (SSA), the
sanitation infrastructure in major cities has been outpaced by
population increases, making the collection and management
of urban wastewater ineffective. In many large cities (for
example, Accra in Ghana), only a small part of the wastewater
produced (�10%) is collected in piped sewerage systems for
treatment (Drechsel et al., 2002).
Owing to the gradual addition of contaminants into
freshwater bodies, and the awareness of their possible
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 2 9
impacts, wastewater treatment is now receiving greater
attention from the governments of several water-scarce
countries and organizations such as World Bank, the Food
and Agriculture Organization of the United Nations (FAO), and
the United Nations Development Programme (UNDP), among
others.
There is now more scope in the water and environment
sector to develop and implement wastewater treatment
technologies that: (1) need low levels of capital investment
for construction, operation and maintenance; (2) maximize
the separation and recovery of by-products (such as nutrients)
from polluted substances; (3) are compatible with the intended
reuse option in that they yield a product of an appropriate
quality in adequate quantities; (4) can be applied at both very
small and very large scales; (5) are accepted by farming
communities and the local population. Bearing in mind that
treated wastewater could be used for agricultural, environ-
mental, recreational and industrial purposes, it is important to
realize that such wastewater must be adequately treated and
used appropriately. This is important for several reasons:
1. T
T
C
A
B
C
Ma
b
c
sd
e
�f
sg
s
he discharge of untreated wastewater into surface water
bodies affects the quality of both the water it enters and the
water further downstream.
2. T
reated wastewater could be used to provide a reliablesource of irrigation water in urban and peri-urban areas,
providing water for parks, play and sports grounds, and
able 4 – Guidelines for microbiological qualities of treated wast
ategory Wastewater reuseconditions
Exposed group ofcommunities
I
Unrestricted irrigation
(all crops, including vegetable
and salad crops eaten
uncooked, sports fields,
public parkse)
Workers, consumers,
public
Any
Restricted irrigation
(cereal crops, industrial
crops, fodder crops,
pastures, and treesg)
B1 workers,
children > 15 years,
nearby communities
Spr
Spr
B2 same as B1 Floo
B3 workers,
children of all ages,
nearby communities
Any
Localized irrigation
(crops in category B,
but without exposure of
workers and communities)
None Tric
odified from Blumenthal et al. (2000) and Carr et al. (2004).
In specific situations, these guidelines may be modified according to local
Ascaris and Trichuris species and hookworms. The guideline values are als
During the irrigation period; routine monitoring is not required if wastew
torage and treatment reservoirs (WSTR).
During the irrigation period; the faecal coliform counts should preferably
Local epidemiological factors may require a more stringent standard for p
200 faecal coliforms 100 mL�1 is appropriate for the lawns.
This guideline value can be increased to �1 if conditions are hot and dry
upplemented with anti-helminthic chemotherapy campaigns in areas of w
In the case of fruit trees, irrigation should stop 2 weeks before fruit is pick
prinkler irrigation should not be used.
roadside greenery. Its other uses may be environmental
(providing water for wetlands, wildlife refuges, riparian
habitats, urban lakes and ponds), or industrial (used in
cooling, boiling, and the processing of materials). It could
also be used as a source of non-potable water to provide for
many needs (fire fighting, air conditioning, dust control, and
toilet flushing). It may also be used for aquaculture and
groundwater recharge—a use, which has received con-
siderable attention in recent years as it needs proper
legislation and periodic monitoring of the aquifer quality.
3. T
he treatment of wastewater before discharging it intosurface water bodies helps to safeguard existing (scarce)
sources of good-quality drinking water and protects the
environment.
4. U
sing treated wastewater for irrigation decreases thedemand for freshwater in agriculture.
5. I
f it is treated and managed appropriately, treated waste-water can be used to provide several nutrients essential
for plant growth. This directly benefits farmers because
they have to make little or no investment in fertilizer
(a significant farm input) or its application.
The benefits of using treated wastewater must also be
considered against the human health, economic, and environ-
mental costs of not using it. For example, treating and using
wastewater would reduce the discharge of untreated waste-
water into the environment (so reducing water pollution and
ewater for irrigationa
rrigationmethod
Intestinal nematodesb
(arithmetic mean;no. per 1000 mL)c
Faecal coliforms(geometric mean;no. per 100 mL)d
�0.1f �103
ay or
inkler
�1 �105
d or furrow �1 �103
�0.1 �105
kle or drip Not applicable Not applicable
epidemiological, socio-cultural, and hydrogeological factors.
o intended to protect against risks from parasitic protozoa.
ater is treated in waste stabilization ponds (WSP) or wastewater
be done weekly, but at least monthly.
ublic lawns, especially hotel lawns in tourist areas. A guideline of
and surface irrigation is not used, or if wastewater treatment is
astewater use.
ed, and no fruit should be picked up from the ground. In addition,
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 210
Table 5 – Recommended maximum concentrations (RMCs) of selected metals and metalloids in irrigation watera
Element RMC (mg L�1) Remarks
Aluminum 5.00 Can cause non-productivity in acid soils (pH < 5.5), but more alkaline soils
at pH > 7.0 will precipitate the ion and eliminate any toxicity
Arsenic 0.10 Toxicity to plants varies widely, ranging from 12 mg L�1 for Sudan
grass to less than 0.05 mg L�1 for rice
Beryllium 0.10 Toxicity to plants varies widely, ranging from 5 mg L�1
for kale to 0.5 mg L�1 for bush beans
Cadmium 0.01 Toxic at concentrations as low as 0.1 mg L�1 in nutrient solution for beans,
beets and turnips. Conservative limits recommended
Chromium 0.10 Not generally recognized as an essential plant growth element.
Conservative limits recommended
Cobalt 0.05 Toxic to tomato plants at 0.1 mg L�1 in nutrient solution.
It tends to be inactivated by neutral and alkaline soils
Copper 0.20 Toxic to a number of plants at 0.1–1.0 mg L�1 in nutrient solution
Iron 5.00 Non-toxic to plants in aerated soils, but can contribute to soil acidification
and loss of availability of phosphorus and molybdenum
Lithium 2.50 Tolerated by most crops up to 5 mg L�1. Mobile in soil. Toxic to citrus
at low concentrations with recommended limit of <0.075 mg L�1
Manganese 0.20 Toxic to a number of crops at a few-tenths to a few mg L�1 in acidic soils
Molybdenum 0.01 Non-toxic to plants at normal concentrations in soil and water. Can be toxic to
livestock if forage is grown in soils with high concentrations of available molybdenum.
Nickel 0.20 Toxic to a number of plants at 0.5 to 1.0 mg L�1; reduced toxicity at neutral or alkaline pH
Lead 5.00 Can inhibit plant cell growth at very high concentrations
Selenium 0.02 Toxic to plants at low concentrations and toxic to livestock if forage is
grown in soils with relatively high levels of selenium
Zinc 2.00 Toxic to many plants at widely varying concentrations; reduced toxicity
at pH � 6.0 and in fine textured or organic soils
Modified from Ayers and Westcot (1985).a The maximum concentration is based on a water application rate, which is consistent with good irrigation practices (10,000 m3 ha�1 yr�1). If
the water application rate greatly exceeds this, the maximum concentrations should be adjusted downward accordingly. No adjustment
should be made for application rates less than 10,000 m3 ha�1 yr�1. The values given are for water used on a long-term basis at one site.
the contamination of drinking water supplies), and would i-
mprove the socioeconomic situation of farmers, and thus their
health and that of their families.
Based on different parameters, various guidelines (Ayers
and Westcot, 1985; WHO, 1989; Blumenthal et al., 2000; Carr
et al., 2004; WHO, 2006) are available for wastewater use in
agriculture (Tables 4 and 5). However, in many developing
countries these guidelines are not followed and most farmers
use untreated wastewater in an unplanned manner to irrigate
a variety of crops. Most cities in these countries have networks
of open and covered interconnected channels located within
and around urban premises. In general, these channels carry a
mixture of wastewater generated by domestic, municipal, and
industrial activities. The farmers divert untreated wastewater
from these channels to provide irrigation water as and when it
is needed. Although farmers irrigate a range of crops with
wastewater, they often prefer to grow high-value vegetables as
a market-ready product, which will generate a higher income
(Qadir et al., 2000).
In some cases, the authorities implementing government
regulations periodically expel these farmers from their fields
(Keraita and Drechsel, 2004) or uproot wastewater-irrigated
vegetables. In other cases, however, the administrators do not
make any efforts to check the use of wastewater in this way.
Rather they regard this farming practice as a viable option for
wastewater disposal. The farmers consider such untreated
wastewater to be a reliable source of irrigation, which involves
less cost than other sources of irrigation water such as
groundwater pumping (Van der Hoek et al., 2002). Other
benefits to the farmers include the fact that farmers have to
invest nothing, or very little, in fertilizer purchase and
application, while benefiting from greater levels of crop
production than are obtained via freshwater irrigation. In
addition, they enjoy higher incomes as a result of cultivating
and marketing high-value crops. These benefits help the
farmers to ensure that their families receive better levels of
nutrition and that their children benefit from better educa-
tional opportunities. For all these reasons, farmers take health
risks and use untreated wastewater when the opportunity
presents itself (Ensink et al., 2002; Matsuno et al., 2004).
Surveys and research studies carried out in different
countries revealed that fields irrigated with untreated waste-
water yielded more than those irrigated with freshwater
(Shende, 1985; Minhas and Samra, 2004; Table 6). In addition,
economic analyses based on the cost of production of different
crops have shown attractive economic returns from waste-
water-irrigated fields in Syria (Qadir et al., unpublished data).
The analyses revealed that each US$ invested in the produc-
tion process gave a return of US$ 5.31 in the case of wheat
(Triticum aestivum L.) irrigated with wastewater and US$ 2.34 in
the case of wheat irrigated by groundwater. In addition to the
higher wheat yields provided by wastewater-irrigated plots,
there were savings with regard to fertilizer use. In comparison
with those growing groundwater-irrigated wheat, the farmers
using wastewater to irrigate wheat saved US$ 95 ha�1. Similar
economic return trends were obtained for faba bean (Vicia faba
L.). However, in the case of cotton (Gossypiumhirsutum L.), there
was little difference between the returns from wastewater
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 2 11
Table 6 – Yields of crops irrigated with good-quality water and untreated wastewater
Crop Crop yield (Mg ha�1) Reference
Freshwater Untreated wastewater
Carrot 9.71 11.75 (+21)a Shende (1985)b
Radish 7.26 8.33 (+15) Shende (1985)
Potato 6.12 9.33 (+29) Shende (1985)
Cabbage 9.27 12.13 (+31) Shende (1985)
Tomato 10.01 13.38 (+34) Shende (1985)
Tobacco 1.12 1.25 (+12) Shende (1985)
Rice 3.80 3.30 (�13) Minhas and Samra (2004)c
Wheat 2.80 3.10 (+11) Minhas and Samra (2004)
Soybean 1.60 2.10 (+31) Minhas and Samra (2004)
Cauliflower 16.40 18.20 (+11) Minhas and Samra (2004)
Sugarcane 42.70 44.40 (+04) Minhas and Samra (2004)
Wheat 3.29 4.49 (+36) Qadir et al. (unpublished data)d
Cotton 4.14 4.24 (+02) Qadir et al. (unpublished data)
a Figures in parenthesis indicate percent increase (+) or decrease (�) in wastewater irrigated crop yield over respective yield from area irrigated
with good-quality surface or groundwater.b Results from Poona Sewage Farm, India.c Results from Nagpur Sewage Farm, India.d Results from a survey of farmers’ fields in Aleppo region, Syria.
irrigation (US$ 5.17) and groundwater irrigation (US$ 5.23) for
each US$ invested. This is because wastewater resources in
the area during the long summer growing season of cotton are
not sufficient to provide the crop with its needs. Therefore, the
wastewater-irrigating farmers also use fertilizers and pump
groundwater as and when needed. The cultivation of
vegetables – which are grown on only 7% of the waste-
water-irrigated area because of government restrictions –
produced the highest economic returns from wastewater
irrigation: US$ 7.48 for each US$ invested. This was much
greater than in the case of vegetables irrigated with ground-
water, where the return was US$ 3.29 per US$ investment
(Qadir et al., unpublished data). Although these crop yield and
economic analyses indicate that communities who use
untreated or partly treated wastewater clearly benefit finan-
cially, there is a need to carry out comprehensive analyses of
the potential environmental and health implications and their
costs. These must be weighed against both the short- and
long-term benefits of wastewater use.
Owing to the low literacy rate found amongst farmers in
developing countries, limited and inappropriate information
gathering and reporting, insufficient public pressure, most
farmers using polluted water in low-income countries remain
uninformed about the health and environmental conse-
quences (Hussain et al., 2002). Moreover, farmers and
authorities have insufficient knowledge about the technical
and management options available for reducing the environ-
mental and health risks associated with wastewater use.
Depending upon the levels of contaminants present, the
continued and uncontrolled use of untreated wastewater as
an irrigation source could have a variety of implications. These
include the following:
1. G
roundwater contamination through the movement ofhigh concentrations of a wide range of chemical pollutants
(Ensink et al., 2002). This is particularly true in the case of
wastewater that contains untreated industrial effluent. The
pollutants reaching groundwater in this way have the
potential to impact upon human health when groundwater
is pumped for direct human consumption. Pathogens have
also been found to accumulate in the groundwater found
immediately beneath wastewater-irrigated fields (Ensink
et al., 2002).
2. T
he gradual buildup, in the soil solution and on the cationexchange sites of soil particles, of ions such as Na+ and a
range of metals and metalloids which are deleterious to the
soil. In this way, potentially harmful metals and metalloids
may reach phytotoxic levels (Qadir et al., 2005). The
accumulation of excess Na+ in the soil can have numerous
adverse effects, including changes in exchangeable and soil
solution ions and soil pH, the destabilization of the soil
structure, the deterioration of the soil’s hydraulic proper-
ties, and an increased likelihood of crusting, runoff, erosion
and aeration. It can also have osmotic effects and specific
ion effects in plants (Sumner, 1993; Qadir and Schubert,
2002).
3. T
he accumulation of potentially toxic substances in cropsand vegetables which will, ultimately, enter the food chain,
so damaging human and animal health. For example, leafy
vegetables irrigated with untreated wastewater containing
metals and metalloids can accumulate higher levels of
certain metals, such as cadmium (Cd), than non-leafy
species (Qadir et al., 2000). Excessive exposure to this metal
has been associated with various illnesses in people,
including gastroenteritis, renal tubular dysfunction, hyper-
tension, cardiovascular disease, pulmonary emphysema,
cancer, and osteoporosis (Wagner, 1993). Numerous ill-
nesses are also associated with the ingestion of excessive
levels of other metals and metalloids. Similarly, pathogens
may enter the food chain via the same pathway. However,
in most cases, industrial pollutants in the form of a variety
of metals and metalloids can cause greater and longer
lasting health effects in people than pathogenic organisms.
4. T
he health risks associated with the presence of parasiticworms, and viruses and bacteria. These have the potential
to cause disease in farming families exposed to untreated
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 212
wastewater for extended periods. Such diseases also raise
the issue of the financial consequences associated with
treatment. Farmers using untreated wastewater for irriga-
tion demonstrate a higher prevalence of hookworm and
roundworm infections than farmers using freshwater for
irrigation. Hookworm infections occur when larvae, added
to the soil through wastewater use, penetrate the skin of
farmers working barefoot (Van der Hoek et al., 2002).
Bearing in mind the challenges associated with the use of
wastewater for irrigation, studies carried out by the research-
ers at the International Water Management Institute (IWMI),
Sri Lanka have proposed a number of options to maximize the
benefits and minimize the risks involved in the use of untr-
eated wastewater for agriculture (Scott et al., 2000; Ensink
et al., 2002; Van der Hoek et al., 2002; IWMI, 2003; Matsuno
et al., 2004; Scott et al., 2004;). These options include: (1) the use
of suitable irrigation techniques and the selection of appro-
priate crops that are less likely to transmit contaminants and
pathogens to consumers; (2) the use of protective measures
such as boots and gloves to control farm workers’ exposure to
pathogens; (3) the implementation of a medical care program
through the use of preventive therapy such as anti-helminthic
drugs; (4) the post-harvest management of vegetables, thro-
ugh washing and improved storage; (5) the conjunctive use of
wastewater and freshwater to dilute the risks and increase the
benefits by supplying nutrients to a larger area; (6) upstream
wastewater management and appropriate low-cost treat-
ment; (7) education and increased awareness among farmers,
consumers, and government organizations; (8) the implemen-
tation of monitoring programs for key environmental, health,
and food safety parameters.
The Hyderabad Declaration on Wastewater Use in Agri-
culture made on 14 November 2002 (available at http://
www.iwmi.cgiar.org/health/wastew/hyderabad_declara-
tion.htm) – which resulted from a workshop organized by
IWMI and the International Development Research Center,
Canada – stressed the need to
‘‘safeguard and strengthen livelihoods and food secur-
ity, mitigate health and environmental risks and
conserve water resources by confronting the realities
of wastewater use in agriculture through the adoption of
appropriate policies and the commitment of financial
resources for policy implementation’’.
The management options used should include raising
public awareness, using safer irrigation methods, minimizing
human exposure, restricting the types of crops irrigated with
wastewater, disinfecting produce, ensuring institutional
coordination, increasing land tenure, and increasing funding
(Scott et al., 2004). In view of the fact that it is not possible to
simply ban wastewater use in many developing countries, the
World Health Organization (WHO) is considering the realities
faced by these countries while revising guidelines for waste-
water use in agriculture (WHO, 2006).
2.3.2. Agricultural drainage waterAdequate drainage is a prerequisite if irrigation is to be
sustainable, particularly when salts in groundwater and high
water tables or waterlogging may damage the crops. A fraction
of the water used for crop production results in drainage
water, which contains salts and the residues of agro-
chemicals such as pesticides, fertilizers, and soil and water
amendments. To maintain an appropriate salt balance in the
topsoil layer, which makes up the effective root zone, the
salinity of the drainage water percolating below the root zone
must be higher than the salinity of the irrigation water applied.
Moreover, saline geological deposits often exist along the flow
path. As drainage water flows through these deposits, the salt
loads in the resulting drainage water can considerably exceed
those projected to occur as a result of irrigation alone (Van
Schilfgaarde, 1994). In some geological settings, drainage
waters may dissolve and displace some minor, but potentially
toxic, elements. As freshwater resources are becoming
increasingly scarce, the reuse of agricultural drainage water
has become an important source of irrigation. Contingent
upon the levels and types of salts present, and the use of
appropriate irrigation and soil management practices, agri-
cultural drainage water can be used for different crop
production systems (Rhoades, 1999; Oster and Grattan, 2002).
Two types of drainage systems (subsurface tile drainage
and tubewell drainage) are practiced on large areas suffering
salt and shallow water table problems. In addition to the
conventional drainage systems used to control water table
depth and salinity, bio-drainage – the use of vegetation to
manage water fluxes in the landscape through evapotran-
spiration – is also used in some areas. Deep-rooted crops and
trees are the best candidate plant species for use as bio-
drainage tools. A combination of bio-drainage and conven-
tional drainage systems might also be considered, depending
on site-specific conditions (Tanji and Kielen, 2002).
Climatic conditions (such as the amount and distribution of
rainfall) and the drainage techniques used all influence crop
response to drainage water irrigation. Under the South Asian
monsoonal climate, and in other areas receiving high intensity
rainfall over a short period, saline drainage effluents could be
used without appreciably reducing crop yields (Sharma and
Rao, 1996). Improved drainage techniques such as controlled
drainage and sub-irrigation can be used to precisely manage
water tables and make better use of drainage water (Sharma
and Minhas, 2005).
Soil characteristics such as texture and the selection of
appropriate crop species play important roles in addressing
elevated levels of salinity and sodicity. Under the South Asian
monsoonal climate, waters with salt concentrations as high as
EC 12 dS m�1 can be used for growing salt-tolerant and
moderately salt-tolerant crops on coarse-textured soils. But
on fine-textured soils, waters with an EC of more than
2 dS m�1 often create salinity problems. In addition, the
leaching requirements of soils increase with the salinity of
the irrigation water and the sensitivity of the crop to salinity
(Kijne, 1996). Crops like beans, sorghum and mustard can
tolerate higher levels of salinity after they have been
established by applying non-saline water before sowing, to
leach down the salts from the root zone (Sharma and Minhas,
2005).
There are two major approaches that can be used to
improve and sustain agricultural production in a salt-prone
environment: (1) modifying the environment to suit the plant,
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 2 13
and (2) modifying the plant to suit the environment. Both
approaches have been used, either singly or in combination
(Tyagi and Sharma, 2000). However, the first approach has
been used more extensively because it enables the plants to
respond better not only to the water used but also to the other
production inputs involved. These approaches provide
socially and environmentally favorable levels of agricultural
production, provided that the characteristics of the water and
the soil, and the intended management and uses of the crops,
are taken into consideration (Tyagi and Sharma, 2000; Qadir
et al., 2003; Oster and Birkle, 2004). Such use of saline waters
may lead to conservative water quality standards being
replaced with site-specific guidelines, which take into account
factors such as soil texture, crop salt tolerance, and irrigation
management (Minhas and Tyagi, 1998).
Grattan and Rhoades (1990) proposed a set of criteria for
selecting the crops that could be grown when reusing
agricultural drainage water. Oster and Birkle (2004) provided
information about the growth habits, salt tolerance charac-
teristics, average root zone salinity at 70% yield, and leaching
requirement of several forages when irrigated with a saline–
sodic water (EC 10 dS m�1 and SAR 15). And, Qureshi and
Barrett-Lennard (1998) revealed useful information regarding
sources of seed, nursery raising techniques, and land
preparation and planting procedures for 18 different tree
and shrub species which demonstrate potential for growth on
degraded land and under salt-prone water conditions. In
addition to conventional agriculture systems and in saline
agriculture, drainage water can also be reused in wildlife
habitats and wetlands and for the initial amelioration of salt-
affected soils.
Two options are available for the conjunctive use of saline
water and freshwater: blended and cyclic use. The cyclic
option involves the use of saline water and non-saline
irrigation water in crop rotations that include both moderately
salt-sensitive and salt-tolerant crops. Typically, the non-
saline water is also used both before planting and during the
initial growth stages of the salt-tolerant crop, while saline
water is usually used after seedling establishment. Blending
consists of mixing non-saline and saline water supplies before
or during irrigation. Blending is a promising option in areas
where freshwater can be made available in adequate
quantities on demand. However, cyclic use is most common
and offers several advantages over blending (Rhoades, 1999).
Analyses of a large number of experiments have shown that at
the same level of water salinity (weighted average salinity) the
yields for different cyclic use modes were higher than the
estimated yields for blending. Surveys indicated that the
farmers alternating saline and freshwater obtained higher
production levels in the cases of both cotton and millet than
did those using both waters in a blended form (Minhas and
Tyagi, 1998).
In addition to cyclic and blended use, drainage water may
be used in a sequential system (Grattan and Rhoades, 1990;
Grattan et al., 2004; Grieve et al., 2004), during which relatively
better quality water is applied to the crop with the lowest salt
tolerance. The drainage water from that field – obtained from a
subsurface drainage system – is then used to irrigate crops
with a greater salt tolerance. The simplest management
method is to use the drainage water on fields, which are
located down-slope from those where the drainage water is
collected. There is no fixed number of times that the cycle can
be repeated. It depends on salinity, sodicity, and concentra-
tions of toxic minor elements in the drainage water, the
volume of water available, and the economic value and
acceptable yield of the crop to be grown. The strategy in
which drainage water with an EC of more than 4 dS m�1 is
sequentially used to irrigate crops and trees (i.e. an agrofor-
estry system) with an increasing salt tolerance is sometimes
referred to as an ‘agro-drainage system’ (Karajeh et al., 1992;
Karajeh and Tanji, 1992a,b). The sequential strategy provides a
means of minimizing the volume of drainage water produced
by irrigated agriculture (Oster and Grattan, 2002). Rhoades
(1989) proposed an integrated strategy that could be used to
facilitate the use of saline water for irrigation, in order to
minimize drainage disposal problems and to maximize the
beneficial use of multiple water sources. Specifically, he
suggested the interception and isolation of marginal-quality
drainage water from good-quality water supplies, so that they
could be used within dedicated parts of an irrigation project as
a substitute for part of the freshwater otherwise used to
irrigate the crops.
The long-term feasibility of using drainage water for
irrigation could be increased when the technique is used on a
project or regional scale, rather than on individual farms.
Grattan and Rhoades (1990) proposed that regional manage-
ment could allow the reuse of drainage water in dedicated
areas, so as to avoid the successive increases that would occur
in the concentration of the drainage water if the reuse process
were to be used with the same water supply and on the same
land area (a closed system). With regard to project-based
management, certain farms could be dedicated to reuse while
other areas, such as upslope areas, could be irrigated solely
with good-quality water as usual. The second-generation
drainage water from the primary reuse area could then be
discharged to other dedicated reuse areas where even more
salt-tolerant crops and agroforestry systems are established
or where brackish water based fisheries exist. The final
discharges of small quantities may then be disposed of via
evaporation ponds or water treatment plants. Ideally,
regional coordination, participatory management, and cost
sharing among all user groups should be institutionalized
when implementing such regional drainage-water-reuse
systems.
2.3.3. Saline and/or sodic groundwaterMany water scarce areas have aquifers of marginal quality,
such as those that contain saline and/or alkali (�sodic) waters.
Saline water contains excess levels of salts, while sodic water
contains elevated levels of Na+ compared to other cations.
Such marginal-quality waters result from reactions with the
layers of earth, or strata, through which the water passes on its
way to becoming groundwater, as well as reactions within the
geologic formations in which the groundwater is located.
Saline aquifers may also occur in the vicinity of seawater (as is
the case in a coastal region). The quality of many groundwater
bodies has been affected by drainage water from agricultural
areas (Bohlke, 2002). In addition to the environmentally sound
and productive use of saline–sodic groundwater, this section
also addresses the development of a water resource.
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 214
Table 7 – Average grain yield of rice and wheat asaffected by conjunctive use of alkali water and fresh-water over a period of 6 years
Treatment Grain yield(Mg ha�1)
Water produc-tivity (kg m�3)
Rice Wheat Rice Wheat
Freshwater (FW) 6.7 5.4 0.62 1.80
Alkali water (AW) 4.2 3.6 0.39 1.20
2 FW–1 AWa 5.2 6.7 0.62 1.73
1 FW–1 AWb 5.3 6.3 0.58 1.77
1 FW–2 AWc 4.8 5.7 0.53 1.60
Modified from Bajwa and Josan (1989).a Two irrigations with freshwater and one irrigation with alkali
water.b One irrigation with freshwater and one irrigation with alkali
water.c One irrigation with freshwater and two irrigations with alkali
water.
Driven by the need to produce more under water-scarce
conditions, larger amounts of saline groundwater are
pumped for irrigation in several countries in the Middle East
as well as in numerous areas elsewhere. For example, India’s
annual net groundwater draft is 135 � 109 m3. Of this
32 � 109 m3 is estimated to consist of saline and/or sodic
water (Minhas and Samra, 2003), which is about one-fourth of
the total volume of groundwater used in the country. The use
of marginal-quality groundwater resources without appro-
priate soil-, crop- and irrigation-management strategies
poses considerable risks, in terms of the development of
salinity, sodicity, ion-specific toxicity, and nutrient imbal-
ances in soils (Sharma and Minhas, 2005). These conditions
reduce crop productivity and limit the choice of crops that can
be grown. However, options are available for the use of saline
and sodic groundwater through the use of improved methods
of water conservation, remediation, development, and
application (Rhoades, 1999; Tyagi and Sharma, 2000; Qadir
and Oster, 2004).
Different methods of irrigation have been used for saline
and sodic groundwater (Sharma and Minhas, 2005). In
comparison with surface irrigation, high-energy pressurized
irrigation methods (such as sprinkler and drip irrigation) are
typically more efficient, as the volume of saline water to be
applied can be adequately controlled. The drip irrigation
system also avoids injury to the leaves of plants and enhances
the threshold limits of the crop’s salt tolerance, by modifying
the patterns of salt distribution and maintaining a constantly
high matric potential in the soil (Tingu et al., 2003). These
authors found that both the yield and quality of watermelons
was greater in a treatment irrigated with saline water (EC 3.3–
6.3 dS m�1) using drip irrigation than in a control treatment.
The greatest improvements in yield and melon quality were
obtained when saline water was applied at a rate equivalent to
60% of open pan evaporation. However, salts accumulated in
the root zone, which caused difficulties when planting
subsequent crops because the salts needed to be effectively
leached using either flood or sprinkler irrigation.
Most past research on the management of saline–sodic
groundwater resources and soils has led to the development of
management practices at the field level, without considering
their implications and practicability in terms of water and salt
balances at the irrigation-system and river-basin levels (Tyagi,
2003). In most of the irrigation systems used in arid and semi-
arid regions, water inadequacies at the tail end are compli-
cated by a gradual decrease in freshwater availability and a
decrease in water quality from the head through to the tail
reaches. For example, in the Bhakra command of the Indian
Punjab, the volume of canal water available decreased from
2500 m3 ha�1 (in the head reach) to 800 m3 ha�1 (in the tail
reach), with a corresponding increase in groundwater salinity
(from 2.5 to 6.8 dS m�1). This situation favored groundwater
pumping by shallow tubewells in the head reach and led to the
transfer of this pumped groundwater to the tail reach (Tyagi,
2003). However, caution needs to be taken that such water
markets may not lead to over-exploitation of the aquifers and
an increase in soil salinity. The potential increase in relative
yield with such groundwater transfer from head to tail reach
of a water course in Batta minor (Bhakra Irrigation System,
India) indicated that relative yield would increase from 0.70 to
0.85 in the entire water course if 50% of marginal-quality
groundwater from the head reach was transferred and used in
the tail reach without changing the canal water allocation
(Chandra, 2001). The relative yield would go up to 0.89 if,
instead of blending, the groundwater was used in a cyclic
mode.
Excessive levels of some of the constituents of the
groundwater used for irrigation, such as Na+, carbonate
(CO32�), and bicarbonate (HCO3
�), can adversely modify soil
characteristics and impact upon crop yields. Continuous
irrigation using waters that contain elevated levels of residual
sodium carbonate (RSC) and which have an elevated sodium
adsorption ratio (SAR) tends to increase the soil’s pH and the
exchangeable sodium percentage (ESP), which in turn
decreases the permeability of the soil to water and reduces
crop yield (Sharma and Minhas, 2005). However, studies have
shown that irrigating crops with sodic water after two
irrigations using freshwater resulted in rice and wheat yields
comparable to those yielded when freshwater irrigation was
used throughout the cropping period (Table 7). The use of
chemical amendments such as gypsum (CaSO4�H2O) is
particularly recommended when RSC values exceed
5 mmolc L�1, soils are medium-textured, and annual rainfall
is below 500 mm (Minhas et al., 2004). Gypsum application
techniques have been refined in the form of ‘gypsum beds’,
the use of which improves gypsum’s solubility and applica-
tion efficiency and reduces the costs of its application. This
method provides considerable savings and produces higher
crop yields (Pal and Poonia, 1979; Sharma and Minhas, 2005).
In California, applying gypsum by mixing it with irrigation
water has been a common practice for several decades. Such
application of gypsum has the potential to improve the soil’s
infiltration rate (Oster et al., 1992).
In some areas, highly degraded salt-prone soils associated
with saline and/or sodic aquifers cannot be ameliorated in a
manner that allows the profitable cultivation of high-value
crops. The best approach to deal with such conditions has
been to retire these areas to permanent vegetation (Tomar
et al., 2002). The preferred choices for tree species in these
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 2 15
areas include Tamarix aphylla (L.) H. Karst., Prosopis juliflora
(Sw.) DC, Acacia nilotica (L.) Delile, Acacia farnesiana (L.) Willd,
and Acacia tortilis (Forssk.) Hayne (Tomar et al., 2002; Sharma
and Minhas, 2005). Several halophytic species, forages, and
field and horticultural crops have also been identified for
biosaline agriculture.
Similar to the development of good-quality groundwater
resources, the development of marginal-quality groundwater
resources can have various negative consequences, such as
groundwater level drawdown, reduced discharge to surface
water bodies, intrusion of lower quality water resources, land
subsidence (Custodio, 2002). Though there seems to be no
single management tool, which can be used to control the
salinity and sodicity of salt-prone land, and the negative side
aspects of water resources development, several practices
interact with each other and should be taken into considera-
tion in an integrated manner to ensure sustainable agri-
culture and livelihoods (Sharma and Minhas, 2005). There
is a need to ensure: (1) the presence of water quantity and
quality monitoring networks and easily accessible databases;
(2) the modification of surface water delivery schedules;
(3) the conjunctive use of multi-quality water resources; (4) the
availability of chemical amendments, as and when needed
and at reasonable costs; (5) the adoption of water-use efficient
irrigation systems such as drip irrigation; (6) the use of
participatory planning by different stakeholders; (7) capacity
building of the national agricultural and extension systems;
(8) an increase in awareness among the farmers, to ensure
a greater understanding of the potentials of plants, soil
and water available, and the uses and markets for the agri-
cultural produce yielded; (9) an adaptive management system
that reacts to environmental and socioeconomic changes
(Loucks, 2000).
3. Opportunities contributing to food securityin water-scarce countries
Opportunities which may be taken advantage of to contribute
to food security in water-scarce countries are: (1) the ‘physical’
movement of water from water-surplus areas, where fresh-
water can be tapped and then transported (in a similar way
that oil is exported from the oil-surplus Middle East to oil-
deficit countries), and (2) the importing of food items from
countries where water resources are adequate and the cost of
food production is relatively low. In the latter case, water-
scarce countries import food items rather than water. This
saves these countries huge amounts of water, which would
otherwise have to be used to produce food domestically
under water-deficit conditions. The same amount of water is
actually used elsewhere in the production process. The terms
‘embedded water’ and ‘virtual water’ have been used to
illustrate the importance of water in the trade in food, which
occurs between water-surplus and water-deficit countries.
3.1. Physical transportation of freshwater
Long-distance, large-scale transportation of freshwater at the
inter- and intra-country scales has been emerging as an
option, which could be used to supplement freshwater needs
in water-scarce areas (Mohsen and Al-Jayyousi, 1999;
Ariyoruk, 2003; Government of India, 2003; Alghariani, 2003).
Several options have been worked out to address long-
distance transportation in MENA. One example is the Great
Man-Made River Project in Libya, which was initiated in the
early 1980s. The existence of vast stores of fossil freshwater in
the southeastern and southwestern desert areas of the
country prompted Libya’s government to build a 3500-km
pipeline to convey water to the coastal areas, where rapid
development and increased populations have placed a severe
strain on the water supply available to households, agricul-
ture, and industry. The pipeline is expected to ship more than
5 � 106 m3 (2 � 109 m3 yr�1) of water across the desert per day
to the coastal areas (Alghariani, 2003). Since the project was
conceived, several economic evaluations have been carried
out and projections have been made of the water transporta-
tion and distribution costs; however, the conclusions reached
differ greatly in each case.
The possibility of moving freshwater long distances from
Turkey to some parts of the Middle East has been discussed
extensively over the last two decades. According to the famous
‘Peace Pipeline Project’, conceived in 1987, Turkey was to
export water to the Middle East, first from the Seyhan and
Ceyhan Rivers (Mohsen and Al-Jayyousi, 1999), and later from
the Manavgat River. Turkey has already finished building a
US$ 150 million anchorage – pumping station and treatment
plant – at the estuary at the mouth of the Manavgat River
(Ariyoruk, 2003). However, political unrest in the region, and
technical and economic complications have greatly hampered
the further implementation of this project. The potential for
projects involving cross-boundary water movement can only
be realized with good regional cooperation and trust among
both water exporting and importing countries and those
located between them.
Outside MENA, China’s water and soil resources are
distributed very unevenly. The basin of the Yangtze River
and the rivers situated to the south of it are considered to be
water-surplus areas, yielding more than 80% of the nation’s
total surface water resources while containing less than 40%
of the nation’s total cultivated land. By contrast, the Yellow
River, Huaihe River, Haihe River basins and the northwestern
inland areas contain 45% of the country’s cultivated land
but possess only 12% of its total water resources, and are
therefore categorized as water-deficit areas. The north-
western and northern parts of China are rich in land and
mineral resources, and provide a production base for energy,
grain, cotton, and edible oil. In these areas, water scarcity has
restricted economic development and induced environmen-
tal degradation. The government has therefore unveiled the
ambitious south-to-north water diversion project, which is
designed to balance the nation’s water supply. The project, a
result of 50 years of investigation and research, aims to divert
water from the Yangtze River valley to the reaches of the
Yellow River, Huaihe River and Haihe River, to ensure an
adequate water supply for farming, industry and other needs
in the north. Estimated to cost more than US$ 22 billion, the
project will have three water diversion routes. Once com-
pleted, it will be able to transport in the range of 38 � 109 to
48 � 109 m3 of water per year to areas containing 300 million
people.
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 216
In recent years, India’s government has also decided to
implement a huge river-interlinking project. The project,
when completed, will consist of 30 links and some 3000
storage points, connecting 37 rivers to form a gigantic South
Asian water grid (Government of India, 2003). Initial project
estimates suggest a staggering cost of US$ 120 billion to handle
inter-basin water transfer of 178 � 109 m3 yr�1 through the
building of 12,500 km of canals. The project is expected: (1) to
create 35 GW (gigawatt) of electricity per year, (2) to add
35 � 106 ha to India’s irrigated areas, and (3) to generate
substantial fishery benefits. A task force has been set up to
suggest possible scenarios, in order to arrive at speedy
consensus amongst the states for water sharing and transfer.
The project is expected to be launched by 2006, and should be
completed in 10 years.
In addition to the cross-boundary transportation of fresh-
water through pipelines, another innovative approach exists
which has recently entered the limelight. This approach
consists of transporting water – using specifically designed,
extremely large, flexible and recyclable, fabric bags – from a
freshwater source across the sea to a coast near to a water-
scarce area. With the capacity of more than 1 � 105 m3, these
huge bags are generally known as ‘medusa bags’, named after
the swimming form of jellyfish often called a medusa. Since
freshwater is less dense than seawater, the cargoes can float
on the sea. Therefore, they will be filled with freshwater to
about 40% of their capacity, before being towed either singly or
in pairs to their destination, where water will be pumped
ashore and the empty bag will be returned to the freshwater
source. Since 1996 a small-scale operation using bags with a
capacity of up to 2 � 103 m3 – 50 times smaller than the
proposed ‘medusa bags’ – have been used to supply water to
the islands of Aegina and Angistri in Greece at half the cost of
previous supplies by tanker. The ‘medusa bags’ offer an option
Table 8 – Estimates of water used to produce different food ite
Food item Water use
Estimate 1c Estimate
Wheat 1000 1150
Rice 1500g 2656
Maize – 450
Soybean – 2300
Palm oil 2000 –
Beef 20000 –
Sheep 10000 –
Poultry 6000 –
Eggs – –
Milk – –
a Quantifying the exact volumes of water needed to produce food items i
to produce a particular food item in different regions. However, these esti
different items.b The average amount of water required to produce cereals in the develo
around 1800 m3 Mg�1.c Allan (1999).d Hoekstra and Hung (2003).e Zimmer and Renault (2003).f Chapagain and Hoekstra (2003) representing the global average for whg In some regions, the amount of water required to produce rice may reh Not reported.
that could be used to transport water from southern Europe to
the southern Mediterranean region (Alghariani, 2003). This
technology appears attractive; however, its use on a larger
scale remains to be proven. Several countries of the
Mediterranean region are assessing its feasibility.
3.2. Food imports and the ‘virtual water’ nexus
Food items have been traded among countries since interna-
tional trade began. By importing food in this way, water-scarce
countries avoid having to use their own water produce the
same amount of food domestically under water-deficit
conditions. They thus ‘save’ this water. The term ‘virtual
water’ has been used to illustrate the important role water
plays in the trade of food between water-surplus and water-
deficit countries (Allan, 1996), which in part have to rely on the
import of food items in order to ensure food security.
Since the term ‘virtual water’ links water, food, and trade
(Allan, 2003), it compares the amount of water embedded in a
crop that can be purchased internationally with the amount of
water that would be required to produce that crop domes-
tically (Allan, 1996). For instance, it takes approximately 1.1 m3
(1 m3 = 1000 L) of water to produce 1 kg of wheat. Thus, for
every kilogram of wheat imported, the water-deficient country
also receives the benefit of about 1.1 m3 (1100 L) of virtual
water, often at a much lower cost than the price (i.e. the value
attached to) the same quantity of water derived from local
water resources in the country itself, if such sources are
available (Chapagain and Hoekstra, 2003). Similar estimates
are available for other food items (Table 8), although
quantifying and comparing the exact volumes of water needed
to produce food items in different agro-ecological zones is
difficult (Rosegrant et al., 2002). The estimates of the ‘virtual
water’ content of food items provide an assessment of possible
msa
to produce food item (m3 Mg�1)b
2d Estimate 3e Estimate 4f
1160 1109
1400 –h
– 463
2750 1716
– –
13500 –
– –
4100 –
2700 –
790 –
s difficult as large differences may exist in the amount of water used
mates give an indication of the amount of ‘virtual water’ contained in
ped world is about 1000 m3 Mg�1 while in the developing world it is
eat, maize, and soybean.
ach 6000 m3 Mg�1 (Rosegrant et al., 2002).
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 2 17
water savings in water-scarce countries. These countries can
optimize water use by importing a proportion of their food
requirements from other countries where water resources are
adequate and available at a lower cost (Allan, 1999).
The global estimates of food production reveal that about
6000 � 109 m3 of soil water and freshwater are mobilized each
year to meet the needs of the world’s 6.5 billion people
(Shiklomanov, 2000). The global volume of international
‘virtual water’ flows is estimated to be 1031 � 109 m3 yr�1,
including 695 � 109 m3 yr�1 from the trade in crops and
336 � 109 m3 yr�1 from the trade in livestock and livestock
products. This means that approximately 13% of the water
used for crop production in the world is not used for domestic
consumption but for export (Chapagain and Hoekstra, 2003).
Including trade in livestock and livestock products, ‘virtual
water’ amounts to about 20% of the global water use in
agriculture. These estimated percentages reflect the situation
on a global scale; the situation varies considerably between
countries.
Worldwide, there is a growing interest in the trade of food
items and ‘virtual water’, partly because of the increasing
importance of food security in countries where water has
become too scarce to meet the demands of continuously
expanding populations (Hoekstra, 2003; WWC, 2004). There-
fore, the role of the food trade is important in MENA, which is
the most water-scarce region of the world. Since the oil boom
of the 1970s and population growth, the average annual rate of
food imports has substantially increased in several Middle
Eastern countries. Based on food trade data for the period
1995–1999, the net amount of water used elsewhere when
producing the crops imported into MENA is estimated to stand
at 74.6 � 109 m3 yr�1 (Chapagain and Hoekstra, 2003). Esti-
mates show that MENA imported about 30% of its food
requirements in 2000 (Allan, 2003). If the trend seen in the
importing of food continues, food imports are expected to
provide 50% of the region’s food requirements in 2050 (Allan,
personal communication, 2002).
The trade in food commodities and ‘virtual water’
combines agronomic, economic, and political aspects. The
agronomic component involves the amount of water used to
produce crops. The ‘virtual water’ perspective is consistent
with the concept of integrated water management, in which
aspects of water supply and demand are considered when
determining the optimal use of limited water resources
(Bouwer, 2002). In accordance with the concept of ‘virtual
water’, there may be a need to modify cropping plans to get
maximum benefits from the available, but limited, water
resources found in water-deficient countries. Apart from the
economic, social, institutional, and political implications,
such cropping plans will also need to consider: (1) water
factors, such as the quantity and quality of the water that is
available to produce crops and the sustainability of water
resources; (2) soil factors, including nutrient availability, and
soil moisture, texture, structure, salinity and sodicity levels; (3)
climatic conditions, particularly temperature, rainfall, and
relative humidity; (4) crop traits, such as water-use efficiency,
adaptability to local conditions, and susceptibility to pests and
diseases; (5) farming aspects, such as the size and productivity
of farms, and the availability of manpower and farm
machinery; (6) economic factors such as the provision of
subsidies for farm inputs, crop insurance and local and/or
international market demand (Qadir et al., 2003).
The economic aspect of food imports and ‘virtual water’
involves the opportunity cost of water use, which is the value
it has when used for other uses (such as the production of
alternative crops or in municipal, industrial, or recreational
activities). The opportunity cost of water use is a key
component of the ‘virtual water’ perspective, and it is
particularly important to consider such costs when seeking
to allocate scarce water resources. Indeed, the economic
aspect of the virtual water concept is closely related to the
comparative advantage concept used in international trade.
This concept suggests that nations should export those
products for which they possess a relative or comparative
production advantage, and should import those products for
which they possess a comparative production disadvantage.
Another economic aspect of the trade in ‘virtual water’
relates to the fact that the grain produced in a water-surplus
country is sometimes traded at less than its production cost.
For instance, in 1996 the price of wheat grain increased to US$
240 Mg�1 (megagram, Mg = 1000 kg) but fell back to US$
140 Mg�1 by May 1997 on the international market. The cost
of producing wheat was estimated to be about US$ 200 Mg�1 at
that time (Allan, 1998). In addition, the world prices of several
food commodities have decreased over the last three decades.
Between 1970 and 2000, for example, the international prices
of three major cereals (wheat, rice and maize) fell by 50–60%.
Over the next two decades, it is projected that the world prices
of most cereals will decline, though more slowly than in the
past (Rosegrant et al., 2002). This means that the economies of
those water-scarce countries that import grains may receive a
subsidized bargain, particularly when the world prices of food
commodities are lower than the cost of production in these
countries.
Many water-scarce countries will continue to rely in part on
imported food items, while also producing domestically a
proportion of the food they require. Thus, the export of
commodities requiring less water will present an opportunity
for those water-scarce countries seeking to maximize the
value of their limited water resources. However, the role of
land and capital in agricultural imports and exports must also
be considered in the case of those countries where these
resources are limited. In addition, labor-intensive crop
production and processing could also provide options in
countries where reducing unemployment is an important
policy objective (Wichelns, 2001). Policies which promote
imports of food (and ‘virtual water’) may have additional
implications: (1) an increased dependency on major exporters;
(2) possible interference by major exporting countries in an
importing country’s internal affairs; (3) effects on local
agricultural production systems and markets; (4) increased
vulnerability to large-scale natural disasters, which could be
exploited by the international food market. Therefore, the
food-importing countries need to consider the policies and
general politics of food-exporting countries while using the
‘virtual water’ trade as a strategic instrument and as an
opportunity to overcome water scarcity and food deficit.
Before 1993, the term ‘embedded water’ (which described a
concept similar to ‘virtual water’) had very little impact as it
failed to capture the attention of the water-management
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 218
community. When Professor J.A. Allan conceptualized the
concept and coined the term ‘virtual water’ in 1993, it had an
immediate impact as people appeared to use it readily as a
useful metaphor. Professor Allan thereafter used the term to
draw attention to the notion that serious local water shortages
could be very effectively ameliorated by global economic
processes (Allan, 1999). He proposed the concept of ‘virtual
water’ as an economically invisible and politically silent way
of solving strategic water problems (Allan, 2001). Use of the
term has been on the increase since 1995, and by the
millennium it had become central to many dialogues relating
to water scarcity and security (Allan, 2003). In the meantime,
the term has received criticism. Considering ‘virtual water’ to
be nothing more or less than the water needed to produce
agricultural commodities, Merrett (2003a) proposed that it
should be replaced with the phrase ‘the crop water require-
ments of food’. Similarly, he suggested that the phrase ‘the
import of food’ should substitute for the term ‘the import of
virtual water’. He considered ‘the import of virtual water’ to be
a metaphorical term, and not a scientific one, and felt that its
use in the arena of policy might lead decision makers to
neglect the current and future status of the agricultural sectors
of food-importing and food-exporting countries. He further
stated that emphasizing food imports as a solution to water
scarcity will result in less production, which in turn will mean
that less water will be required for irrigated agriculture in
water-scarce regions. It was felt that regional politicians could
deflect attention from such dependency, and that the
availability of imported food could allow them to postpone
new water supply initiatives and delay difficult decisions
about the demand management of their water resources.
Merrett therefore felt that one cannot generate accurate and
meaningful recommendations regarding policies that influ-
ence agricultural production, livelihoods, food security, and
international trade based only on a metaphor (Merrett, 2003b).
However, amid appreciation, caution, and criticism (Allan,
2003; Lant, 2003; Merrett, 2003a; de Fraiture et al., 2004), the
metaphors ‘virtual water’ and ‘virtual water trade’ have been
in use for almost a decade. The coming decade may determine
whether they retain their place in the terminology of water
professionals.
4. Future perspectives
Although agriculture will remain the dominant user of water,
in water-scarce countries intense competition for good-
quality water among the different water-use sectors is
expected to reduce the amount of freshwater allocated to
agriculture in the foreseeable future. Whatever the case, there
should be no anxiety in any region of the world, including
MENA, about the availability of water for drinking and
domestic use and for the needs of almost all of the industrial
and service sectors. In fact, these sectors use less than 25% of
the freshwater resources available (Bouwer, 2000). However, to
foster the sustainable management of water resources and the
livelihood of rural communities, water use in agriculture must
be made more efficient. As the situation currently stands,
despite improvements in existing water-use efficiency tech-
niques, water-scarce countries are expected to become
increasingly reliant on non-conventional water resources
and the other opportunities available to augment water
supplies, in order to achieve food security.
Currently, desalination of seawater and highly brackish
groundwater provides 11 � 109 m3 of high-quality water per
year. With regard to drinking water production, the current
costs of desalination and desalinated water distribution are
affordable in many developed and oil-rich countries. However,
it remains an expensive option for use in conventional crop
production systems. And, in developing countries, even
drinking water produced in this way is an expensive resource.
Although it is generally thought that the costs involved in
desalination will decrease further, they will not decrease by an
order of magnitude at any time in the near future. Since
desalination does have environmental implications, it is
important to ensure that adequate environmental regulations
and practices are put in place to ensure that the long-term
disposal of by-products of desalination (such as impurities and
residual water in the form of brine dumped in nearby areas or
into the ocean) will not have adverse environmental impacts.
Interest in rainwater harvesting techniques has increased
in water-scarce countries, and use of these techniques has the
potential to increase rainwater-use efficiency. The effective-
ness of rainwater harvesting is based on several on-site
factors, such as landscape topography, soil surface texture
and structure, the presence of crusty layer or surface
preparation, soil nutrient availability status and the depth
of the cultivated area. While many case studies have shown
tremendous improvements in crop production through
various rainwater harvesting techniques, it is still unclear if
these techniques will be widely adopted by farmers and
pastoralists in the dry areas.
Marginal-quality water resources are valuable in water-
scarce countries. However, the associated health and envir-
onmental risks mean that the use of untreated or inadequately
treated wastewater will need to be curtailed in water-scarce
countries. Given the water scarcity they face, the cost of
treating wastewater in these countries could be more
attractive than the option of developing new supplies for
different water-use sectors. In addition, wastewater treatment
will also lead to gains in terms of environmental conservation.
However, because governments allocate few funds to waste-
water treatment and with private sector involvement lacking,
it will be extremely difficult to enforce the treatment of all the
wastewater generated in resource-poor countries. Therefore,
steps must be taken to maximize the benefits and minimize
the risks involved in wastewater use in agriculture. This will
require international research, development and donor
organizations and national governments to collaborate more,
in order to allocate adequate funding to wastewater treatment
and the education of stakeholders.
There is emerging evidence that the use of saline and/or
sodic waters in conjunction with the adoption of appropriate
soil, crop, and irrigation management strategies can boost
agricultural productivity far more efficiently than was pre-
viously thought (Oster and Wichelns, 2003). The future use of
cyclic, blended, and/or sequential strategies for using these
waters is expected to increase (Kijne, 2003). As a result, existing
soil and crop management practices will need to be modified in
order to cope with the inevitable increases in soil salinity and
a g r i c u l t u r a l w a t e r m a n a g e m e n t 8 7 ( 2 0 0 7 ) 2 – 2 2 19
sodicity that willoccur. Inaddition, the assessment of thefuture
sustainability of using saline–sodic waters, in regard to
maintaining soil permeability, will become a more serious
issue. Although currently available simulation models can be
used to provide insights into what may happen in the future,
such models make use of various simplifying assumptions
when representing complex systems. At present, therefore,
their ability to predict the impacts that soil sodicity and salinity
will have on the permeability of the soil to air and water is
limited. The hydro-salinity models available require field-scale
testing on a range of soil types, and with various irrigation and
cropping practices. Although models are unlikely to replace
entirely the need for continued research into the management
of salt-prone waters and soils, they will provide an important
tool for use when developing alternative management plans
and designing monitoring strategies to track their progress.
Such models may also help researchers to assess the viability of
different drainage water and groundwater reuse strategies and
to extend the results obtained to broadly similar locations
elsewhere.
It is evident that water-scarce countries are unable to
meet their food requirements using either the conventional
or non-conventional water resources available within their
boundaries. Alternative options for contributing to food
security in these countries are provided by the transporta-
tion of water from water-rich areas and the import of food
items from other countries where water resources are
adequate and the cost of food production is relatively low.
However, projects involving cross-boundary water trans-
portation can only realize their potential if there is a good
level of regional cooperation and trust among the water
exporting and importing countries and those located
between them. In addition to other economic and political
considerations, interregional issues may arise when tapping
shared aquifers, and these may strain relationships among
neighboring countries.
Based on the international trade in crops, it is expected
that many water-scarce countries will continue to rely partly
on the import of food items, while producing a proportion of
their food requirements domestically. Water-scarce coun-
tries seeking to maximize the value of their limited water
resources could export commodities, which require less
water to produce. The trade in food will play an important
role in efforts to achieve food security in regions like MENA in
the future, as food imports are expected to provide 50% of the
region’s food requirements by 2050. In fact, the global trade in
food is expected to increase in the foreseeable future. Under
this scenario, the food-importing countries need to consider
the implications that policies in food-exporting countries
may have for them, while using the trade in ‘virtual water’ as
a strategic instrument and an opportunity to overcome water
scarcity. The implications of this are that there would need to
be understanding among the food-exporting and the food-
importing countries. This may require the implementation of
international controls, similar to those in place for oil
trading.
There are several examples of the increased use of non-
conventional water resources by the farming communities in
CWANA, which are faced with the challenge of water scarcity.
This suggests that there is a need for community-based
integrated water resources management. If strategies and
technologies are developed using the accumulated wisdom of
such communities, not only will people’s participation be
enhanced, so will adoption of the new measures. Although
there are no fixed procedures for ensuring that people
participate in such schemes, Sharma and Dixon (1995)
proposed seven steps which provide valuable guidelines: (1)
community immersion, (2) community mobilization, (3)
gender equity, (4) community envisioning, (5) vision valida-
tion, (6) diagnostics and resource community participatory
planning, and (7) participatory monitoring and evaluation
and refinement. In arid and semi-arid areas of the developing
world, particularly CWANA and South Asia, international
agricultural research centers such as IWMI and ICARDA are
collaborating with key stakeholders to address the challenges
relating to water scarcity and to develop appropriate
strategies for the efficient use of non-conventional water
resources.
Acknowledgments
This publication is a part of the joint initiative of the
International Center for Agricultural Research in the Dry
Areas (ICARDA) and the International Water Management
Institute (IWMI) for the assessment and management of
marginal-quality water resources and salt-affected soils. We
gratefully acknowledge the helpful comments of P. Drechsel,
M. Al-Zaeim, and R.J. Thomas on an earlier version of the
paper as well as those from the external reviewers, and J.D.
Oster, Co-Editor-in-Chief of Agricultural Water Management.
Thanks are also due to SCRIPTORIA Writing Services for the
editorial services they provided.
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