Directory UMM :Data Elmu:jurnal:A:Agricultural Water Management:Vol45.Issue3.Aug2000:

Agricultural Water Management 45 (2000) 275±296

Nutritional water productivity and diets
D. Renaulta,*,1,2, Professor W.W. Wallenderb
a
Irrigation Engineer, International Water Management Institute, P.O. Box 2075, Colombo, Sri Lanka
Departments of Land, Air and Water Resources (Hydrology Program) and Biological and Agricultural
Engineering, University of California, Davis, CA 95616, USA

b

Accepted 26 October 1999

Abstract
The increase in water productivity is likely to play a vital role in coping with the additional
requirement for food production and the growth of the uses of water other than in agriculture in the
coming century consistent with the shift from productivity per unit land to productivity per unit
water, the nutritional productivity of water is calculated as energy, protein, calcium, fat, Vitamin A,
iron output per unit water input.
Nutritional productivity is estimated in the agricultural context of California for the main crops
and food products. In general vegetal products are much more productive than animal products.

Four crops emerge as highly productive for one or several key nutrients: potato, groundnut, onion
and carrot. A balanced diet based on these four crops requires a consumption of water
(evapotranspired) of 1000 l per capita per day, while the current needs for the diet in the USA is
5400 l, and 4000 l for developed countries.
On the basis of nutritional productivity analysis it is further demonstrated that a signi®cant part of
the additional water resource to produce food for the next century population can be generated by
changes in food habits. A reduction of 25% of all animal products in the developed countries' diet
generates approximately 22% of the additional water requirements expected by the year 2025.
# 2000 Elsevier Science B.V. All rights reserved.
Keywords: Water productivity; Nutrition; Diet; Food Production; Water requirements

*
Corresponding author. Tel.: ‡33-38824-8224; fax: ‡33-383388-248284.
E-mail addresses: d.renault@engees.u-strasbg.fr, d.renault@cgiar.org (D. Renault), wwwallender@ucdavis.edu
(W.W. Wallender)
1
Tel.: 94-1-867404; fax: 94-1-866854.
2
ENGREF. Montprllier, France, for the early stages of this study.

0378-3774/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 3 7 7 4 ( 9 9 ) 0 0 1 0 7 - 9

276

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

1. Introduction
At the turn of the third millennium there is a growing awareness that water is one of the
crucial limiting factors for increased food and fiber production to supply an ever growing
number of people under increasing competition with other users of water (municipal,
industrial, environmental, etc.). The fundamental question, which underlies current
debates in many forums is: how many people can the planet sustain, given our limited
availability of natural resources?
The answer will obviously depend to a large extent on the availability of water for both
rainfed and irrigated agriculture, the size of the human population and ultimately the
water requirements to grow crops and produce food. The irrigated areas contribute a
major fraction of the global food supply. However, the possibility of expanding the
irrigated areas is becoming rare and costly (Carruthers et al., 1997), therefore, improving
productivity within the existing irrigated areas and within the rainfed agriculture is

crucial. The concept of productivity has, in recent decades shifted from `Crop per unit
area' to `Crop per unit volume of water'. The step sustaining the human population is
nutrition per water volume.
In this paper, nutrition per water volume is quantified in the context of improving
human food production given our limited water resources and modified diets are
evaluated. Water productivity is expressed in kg/m3 whereas nutritional water
productivity is expressed in nutritional units/m3 (nutritional units being energy, protein,
calcium).

2. Water productivity
The concept of productivity, i.e. production per unit input, focuses on limiting factors
or constraints. In the mid-70s, for example, the petroleum crisis highlighted the
importance of energy in agriculture and the productivity of energy became popular. In
areas where labor is constrained, due to rural migration, the concept of labor productivity
is used. Water is also a limiting resource and various productivity measures have been
suggested.
The concept of water productivity is certainly not new. There is a long history of the
development of efficient techniques for managing scarce water in arid areas. Even the
case of the Indus basin development in the 19th century, relies on the concept of water
productivity. In this case, the water delivery was purposely designed to meet only 1/3 of

the command area water requirements because the operational goal was to reach as many
farmers as possible within the available water resource. The productivity indicator of the
development was then the number of farmholdings per unit of water.
The development of large projects after World War II, temporarily led to the illusion
that water is limitless. During the 1970s, the world community again realized that water
resources are limited. It was at this time that, for example, breeders and geneticists
developed a better understanding of the water use during photosynthesis (Stone, 1975).
The difference in water use between C3 and C4 plants and the consequences on total
water use were documented. A C3 plant (wheat, barley, rice, potato) produces 1 tonne of

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

277

dry matter with 600 tonnes of water, while a C4 plant (maize, sorghum, sugarcane)
requires only 300 tonnes (Tinus, 1975). The ratio of the photosynthesis and the
transpiration expresses the water-use efficiency of the crop. This ratio is related to both
the gradient of CO2 at the leaf surface between the inside and outside, and the resistance
of the mesophyll for carbon dioxyde. C4 plants have a higher gradient and a lower resistance than C3 plants, and therefore, a much better water-use efficiency (Feddes, 1988).
Agronomists evaluate the productivity of water through water use efficiency (WUE),

the ratio of yield to water consumed (kg/m3) by the crop through evapotranspiration at the
field scale (Doorenbos and Kassam, 1979) or as the yield per unit depth of water depth
per area (kg/ha/mm) (Gregory, 1991). Biomass yield may also include straw and roots
when the latter have an economic value (Gregory, 1991).
Water use efficiency concepts have been applied in diverse contexts for both rainfed
and irrigated agricultures (Shalhevet et al., 1992). Water productivity in irrigation was
debated during the late 70s and early 80s in India (Sundar and Rao, 1984; Chambers,
1985). More recently, studies on water efficiency and productivity have expanded to
include `real' or `virtual' water savings, and the necessity to analyze the problem at the
water basin level (Seckler, 1996) as well as advocating a consistent approach of water
accounting (Molden, 1997; Young and Wallender, 1999).
In a water scarce country such as Israel, water productivity has significantly increased
from 1.60 kg/m3 in 1949 to 2.32 in 1989 (Stanhill, 1992). This has been made possible by
increases in the water application efficiency at the field scale. Stanhill then identifies
plant breeding as the main avenue to further increase water productivity.
2.1. Models
Productivity may be estimated as the ratio of the output of an economic unit and the
inputs:
PRODUCTIVITY ˆ

OUTPUTS
INPUTS

(1)

Herein, assume water is the limiting input and calculate output. Water productivity is
based on the ratio of mass produced (actual yield, Ya) to the water consumed (actual
evapotranspiration ETa). This productivity is often expressed in kg/m3 and is increasingly
used to measure performance for irrigation systems. A more comprehensive approach for
productivity (Molden et al., 1998) introduces the economical value of the agricultural
production ($/unit of water). Performance comparisons among irrigation systems
producing different crops in different environments are thus possible.
2.2. Average and marginal productivity
Productivity is estimated as an average value for the whole cropping season, i.e. actual
yield (Ya) divided by actual water evapotranspired (ETa) as follows:
Average Productivity ˆ

Ya
ETa

(2)

278

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

Although the average productivity facilitates a comparison between crops and products, it
is not suf®cient to fully express the yield response to water. The marginal productivity, in
contrast, re¯ects the productivity of an additional unit of water, as follows:
Marginal Productivity ˆ

d Ya
d ETa

(3)

The marginal productivity of water is crucial in determining the optimal allocation of
scarce water. In a rainfed system, an increment of water can be applied either as
supplemental preventative irrigation or as an emergency irrigation to avoid crop failure.
In an irrigated system when shortages occur, more sensitive crops and yield sensitive

periods have ®rst priority.
2.3. Water input
In general water productivity is a function of water applied which depends on space
scale and generally increases from small plots to large agricultural domains at a basin
scale because applied water is recycled and reused. Herein, the domain under
consideration is the field scale. We consider water supply through direct precipitation
and/or through irrigation and we are interested in the fraction of applied water which is
consumed by evapotranspiration. We assume crop transpiration and direct soil
evaporation as the water input of the process. Other components such as runoff and
percolation, or losses along the water delivery infrastructure are not accounted for.
2.4. Yield
The yield response to water is highly dependent on the yield response factor (ky)
linking evapotranspiration to yield. The relationship between relative yield decline and
relative evapotranspiration deficit is linear for a range of deficits which do not lead to
crop failure. This relationship is (Doorenbos and Kassam, 1979):




Ya

ETa
ˆ ky 1 ÿ
1ÿ
Ym
ETc

(4)

where Ya is the actual harvested yield, Ym the maximum harvested yield, ky yield response
factor, ETa the actual evapotranspiration, and ETc the potential crop evapotranspiration.
The yield response factor (ky) varies from one crop to another, and from one vegetative
period to another. Doorenbos and Kassam (1979) states that maize is much more sensitive
to water stress (ky ˆ 1.25) than groundnut (ky ˆ 0.7). Therefore, in the case of water
shortages priorities for water distribution should be based on the yield response factor
along with other considerations such as market prices. For crops having a yield response
factor below unity, the maximum water productivity is obtained for a water supply and a
yield less than the maximum values, as recorded by Maozheng and Wang (1992) for a
winter wheat in north China. For most crops the yield response factor reaches a peak
during the flowering period.

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

279

2.5. Interventions for improving water productivity
Classically productivity improvements can result from raising the efficiency of the
input (better timing, minimizing process losses) and increasing the output, as it can be
seen in Eq. (1). One input intervention is to minimize non-beneficial water depletion, i.e.
reducing direct evaporation at the field level particularly during the early stages of crop
development when ground cover is incomplete. For example, DeTar et al. (1996)
compared the productivity of different techniques of irrigation on potatoes. In the same
environment and for the same climatic year they recorded productivity values ranging
from 6 kg/m3 for sprinkler irrigation to 10.5 kg/m3 for subsurface drip irrigation
(accounting in both cases for a limited contribution of rainfall). Another input
intervention is precisely timing water stress. For certain crops the optimum yield
quantity and/or quality occurs when water needs are met at 100% except for a slight water
stress at later stages of development. Another intervention on the water supply is to
increase the reliability of the deliveries to the field. This reduces productivity decline
linked to fluctuating and unpredictable inputs which may occur in rainfed agriculture and
unreliable irrigation systems.

On the other term of the productivity function (output) intervention should consist of
minimizing the effect of other limiting factors (nutrients, pest control) and closing or
optimizing the gap between actual yield (Ya) and maximum possible yield (Ym). It should
also consider developing varieties better adapted to the rainfall pattern to avoid water
stress, and introducing more productive varieties (increase Ym), crops better adapted to
the environment, and/or with a higher economical value.
As mentioned earlier there are situation for which the priority should be to reduce the
gap between (Ya) and (Ym) with improved management of all the inputs including water
(reliability). Herein we assume (Ya) is already optimized, which generally means close to
but not necessary equal to (Ym) and we specifically investigate the improvement of water
productivity in terms of nutritional outputs.

3. Transition to nutritional water productivity
The meaning of water productivity and the decisions related to the concepts of
productivity vary significantly from the point of view of a farmer, an irrigation manager,
an agricultural professional, and a policy maker at national or international levels. In an
open market, the productivity in kg/UW (unit of water), Gross product/UW, Net benefit/
UW are certainly relevant for farmers and local managers and ultimately positive net
benefit is required.
For national policy makers kg/UW or $/UW are worthy variables to maximize. In an
open market, one strategy is to domestically produce and export high value crops and
import low value crops. Alleviation of malnutrition is an issue of production and of
distribution as well as poverty. Nutritional productivity becomes important for some
strategic products and/or in situations of crisis, e.g. whenever the circulation of food is
locally reduced by the closure of boundaries, or if the surplus of the staple food from the
producing countries is no longer able to match the demand. The food shortages at the

280

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

beginning of the seventies, with the rapid increase of basic food prices led to starvation of
the poorest of the poor (Islam, 1995).
For international policy makers, the focus should be more on a comprehensive
approach of productivity, balancing kg/m3, $/m3 and ultimately nutritional productivity.
Furthermore, consideration of the sustainable human population on this planet should
focus on diet and its relation to scarce water resources. The agricultural and dietary policy
are center stage in the strategy for agricultural outputs and nutritional yields, and on the
water requirements per capita.
3.1. Nutrition productivity
Altering yield objectives from weight to nutritional values involves the consideration
of numerous nutritional components of food. It is quite common in nutrition guidelines
and food surveys to consider three metrics: energy, protein and fat (FAO, 1990). In
addition experts list vitamin components, 10 mineral components, four indicators for
lipids, and finally 18 amino acid components (Dunne, 1990).
In this study we purposely limit the approach to the three major components: energy,
protein, and calcium, with additional consideration of fat, iron and Vitamin A. Energy
and protein are the most common components considered in food studies. Calcium, iron
and Vitamin A are considered herein because most nutrition studies show growing
evidence linking malnutrition to deficiencies in these elements. We fully admit that this
approach limited to six components may not be sufficient in some cases, but the method
is expandable.
Although the average productivity per crop or product is assumed, further detailed
investigations should be made using marginal productivity of water with respect to
nutritional outputs for each component. For example a decrease in mass may not lead to a
similar decrease in nutritional outputs and vice versa.
3.2. Water requirements
The estimates of water productivity refer to values of crop yield and water
consumption measured or assessed in California. This agricultural domain is considered
one of the more productive in the world. Therefore, figures for yields must be considered,
in most cases, as representative of the practical maximum sophisticated infrastructure.
Other inputs also do not generally limit yield. Water productivity in this region is not
necessarily representative of a situation where water is more scarce however. It might be
more representative of a standard situation with a good irrigation system. Results are
derived from a database and a spreadsheet model built in 1993 (Barthelemy, 1993). The
Reference Evapotranspiration is estimated using the FAO `CROPWAT' program (FAO,
1993) and planting dates and crop coefficients from the University of California
Cooperative Extension Leaflets (Snyder et al., 1989). Estimates were made for crops
which were planted on more than 5% of each county's total area. The state average for
each crop was estimated from the county values. For crops not grown in California, water
consumption was estimated as if they were grown in the state. Maximum yield estimates
were found in California (California Agricultural Statistics Source, 1991a, 1991b, 1992)

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

281

and US statistics (US Department of Commerce, Bureau of Census, 1989) publications.
For animal products, water consumption for each end product, has been computed
considering each feed component entering the diet during the different stages of the life
cycle of the animal (Barthelemy, 1993). Water productivity (kg/m3) is computed first for
each feed component, including irrigated pasture, rangeland, hay, by-product and cereals.
Then all the water consumed in feed and direct consumption during the life cycle of the
animal is added. This completes the first step of estimating the water requirements which,
along with the yield, allow the evaluation of the water productivity in kg/m3 or the water
requirements in m3/kg. Water productivity in kg/m3 for each product and food category is
given in Tables 1 and 2.

4. Nutritional water productivity
4.1. Model
Nutritional water productivity is:
NWP ˆ

Ya
NP
ETa

(5)

where NWP is the nutritional water productivity (nutrition unit/m3 of water), Ya the actual
harvested yield (kg/ha), Eta the actual evapotranspiration (m3/ha), and NP is the nutrition
content per kg of product (nutrition unit/kg).
In estimating NWP, one source of uncertainty is the ratio yield per water consumed (Ya/
ETa). Another source of uncertainty is the nutrition content of the product (NP) in which
there are significant deviations between data sets. For example the energy content of
cereals varies from 2700 kcal/kg (FAO Balance sheets, 1995) to 3500 kcal/kg (Dunne,
1990) for the US. Part of the variation is explained by differences in processing (raw
product, partially processed, after cooking). Unfortunately most values reported in the
literature are given without any clear specification of level of processing. To overcome
this inconsistency relative nutrition values and relative water savings generated by a
change of diet are used to study policy changes. The values used in the FAO Balance
Sheets are typically 20% lower than those published by Dunne (1990). One possible
reason is that the FAO data set accounts for losses between the raw product and the
consumed product.
To be consistent, the California agricultural context used the same data source for
production, diet and nutrition (FAO, 1998). For components not incorporated in the FAO
database (calcium, iron and Vitamin A) we used values from Dunne (1990), multiplied by
the same correcting factor (0.8) linking the two data sets (energy). Meat productivity is
the average nutritional value considering different parts of the carcass.
4.2. Energy
Energy (kcal/m3) productivity is given in Table 3 and displayed in Fig. 1 for the main
food products usually considered in the FAO balance sheets. It is not surprising that the

Table 1
Crop evapotranspiration, yield, water use ef®ciency estimates for Californiaa
Crops

Cereals
Wheat

Estimates for
California

Other set of data±Maximum
Yield Ym

Etc(mm)

FAO33
Worldwide
(Tonnes)a

Ym
California
(Tonnes)

BRL
France
(Tonnes)b

California versus
other for Ym

IWMI 16
countries
(Tonnes)c

Water use efficiency (WUE)
California
(kg/m3)

FAO33
Worldwide
(kg/m3)a

BRL
France
(kg/m3)b

California estimates
versus other for WUE
IWMI 16
countries
(kg/m3)c

627

5.4

4±6

5.5

5 to 6

Same

0.86

0.8±1

1200
696

8.5
9.8

6±8
6±9

9.5

6.7±7.8
6.6±10

Same
Same

0.71
1.41

0.7±1
0.8±1.6

1.44

0.94
1.20

425

40.4

15±35

27±30

HIGHER

9.51

4±7

10.00

6.40

Sugar beet
1112
Other
Cotton
873
Sugarcane
2491
Soybean
803
Beans
548
Vegetables
Tomatoes
622
Onions
711
Fruit and Nut
Orange
973
Lemon
973
Grapefruit
935
Apples
1037
Grapes
850

57.6

40±60

60

Same

5.18

6±9

HIGHER except
for BRLd
SLIGHTLY LOWER

2.2
97.4
2.6
2.7

4±5
50±150
1.5±2.5
1.5±2

3.2
107±120
2.8±3.0
1.2±1.5

LOWER
Same
Same
HIGHER

0.25
3.91
0.32
0.59

0.4±0.6
5±8
.4 to .7
0.3±0.6

0.76
0.89

0.50
6.50
0.90
0.60

LOWER
LOWER
LOWER
Same than FAO

47.8
49.2

45±65
35±45

60
44

30±40

Same
HIGHER

7.69
6.94

10±12
8±10

13.13
9.30

12.00

LOWER
LOWER

25.7
28.3
32.6
26.8
18.7

25±40
25±40
25±40

Same
Same
Same
Same
Same

2.65
2.91
3.49
2.58
2.20

2±5
2±5
2±5

18

30
30
30
27
11±19

Banana
Groundnut
Almonds

32.0
2.6
1.5

40±60
3.5±4.5

3.5±4.7

Same
LOWER
Same

2.00
0.39
0.13

2.5±4
0.6±0.8

Rice
Maize
Roots
Potatoes

1597
655
1210

15±30

25

3.25
2.5

1.5

2±4

1.60

6.00

0.37

2.40
3.30

Same FAO lower than
IWMI
Same
Same

Same
Same
Same
Same
Same than FAO lower
than IWMI
LOWER
LOWER
LOWER

Forages
Alfalfa (dry) 1238
Maize silage 696
(green)
Small grain
606
hay(dry)
Irrig. Pasture 1244
(dry)
Rangeland
1244
a

13.7
50.4

13

Same

1.11
7.24

5.1

0.84

9.0

0.72

2.2

0.72

FAO 33 after Doorenbos.
BRL: Data recorded in the South-east of France (BRL, 1985).
c
IWMI: Data from a survey of 16 irrigation systems world wide made by IWMI (Molden et al., 1998).
d
Average yield of potato in U.K. in 1990 ˆ 40 tonnes/ha (Bailey, 1990).
b

1.5 to 2

1.59

LOWER

284

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

Table 2
Water requirements per kg and per type of food product (reference to California)
Type of food product

Water requirement (m3/kg)

Vegetables
Cereals
Fat products
Fruits
Nuts
Milk
Poultry and Pork
Bovine meat

0.15
0.7±1.4
11±18
0.45
2.5±4.8
0.8
4.3
13.5

energy productivity of animals is low (between 100 kcal/m3 for bovine meat to about
400 kcal/m3 for pork meat and 660 kcal/m3 for milk) and conversely cereals are high
(from 2300 kcal/m3 for wheat to 3900 for maize). Potatoes (5600 kcal/m3) are the most
productive.
If a person requires an average of 2700 kcal/day then maize and potatoes cover the
daily needs with much less than 1 m3 per capita daily. Wheat, rice, sugarbeet, groundnut
and onions require little more than 1 m3 to produce the daily energy requirement.
4.3. Protein
Estimated protein productivity is given in Table 3 and displayed in Fig. 2. It is no
surprise that the meat group is more productive in protein than in energy. It ranges from
10 g/m3 for bovine meat, i.e. 13% of the daily requirements (75 g of protein), to about
40 g/m3 for egg and milk, i.e. 53% of the daily requirements. Potatoes again appear to be
by far the most productive protein source (150 g/m3). It supplies the daily protein
requirements with only 0.5 m3 of water. Wheat, maize, pulses, groundnut and vegetables
including tomatoes, onion and others supply the daily requirement using less than one
cubic meter of water. Rice is lower than wheat in protein (49 g/m3) and is equivalent to
eggs and milk.
4.4. Calcium
The situation for calcium productivity is quite different from the previous metrics
(Fig. 3). Onions (1673 mg/m3) produce by far the most calcium per unit of water used,
twice the daily need of 800 mg/m3. There are other vegetables such as cabbage,
cauliflower and leeks, which exceed 1500 mg/m3 (not shown in Fig. 3). One product high
in calcium is milk (1233 mg/m3) and all the derived milk products are high in calcium per
unit of water used.
4.5. Fat
There are no recommendations for fat as a whole, although one can find specific
recommendations for some particular lipid components. For example Dunne

Table 3
Nutrient content (NP) and nutritional water productivity (NWP) for main food products
Product

0.863
0.710
1.408
9.524
0.710
0.350
0.210
0.393
0.066
0.087
7.692
6.826
2.646
2.907
3.497
2.004
2.584
2.392
0.602
2.198
0.074
0.217
0.244
0.370
1.266
0.056

Nutrition entry tablea

Nutritional productivity

Outputs per kg product

Nutrional Ouputs per water m3

Cal
(Kcal/kg)

Prot
(g/kg)

Fat
(g/kg)

Calcium
(mg/kg)

Cal
(kcal/m3)

Prot
(g/m3)

Fat
(g/m3)

Calcium
(mg/m3)

2641
2800
2738
591
3548
3397
2482
6067
8337
8320
184
331
250
173
158
216
441
475
1213
617
1376
1879
1354
1402
521
7280

86
69
55
16
0
218
66
283
0
0
8
12
5
0
0
6
2
0
0
6
135
97
135
110
32
13

10
7
12
1
0
12
215
526
939
936
1
0
0
0
0
0
2
0
0
0
89
162
86
98
30
816

324
186
44
57
808
1353
377
753
7
0
26
245
210
145
58
14
54
70
144
92
39
33
59
448
974
191

2279
1989
3856
5626
2520
1188
521
2382
547
721
1416
2259
663
504
553
432
1140
1136
731
1356
102
408
330
519
659
404

74
49
77
150
0
76
14
111
0
0
65
85
13
0
0
11
6
0
0
14
10
21
33
41
40
1

9
5
17
9
0
4
45
206
62
81
11
0
0
0
0
0
6
0
0
0
7
35
21
36
38
45

279
132
63
543
574
473
79
296
0
0
200
1673
556
423
204
29
141
168
87
202
3
7
14
166
1233
11

Nutritional contents are taken from FAO Balance Sheets (USA 1995) for Energy, protein and fat and from Dunne (1990) for calcium (with a correcting factor).

285

a

1159
1408
710
105
1408
2860
4768
2547
15240
11542
130
147
378
344
286
499
387
418
1660
455
13500
4600
4100
2700
790
18000

Productivity
(kg/m3)

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

Wheat
Rice
Maize
Potatoes
Sugar beet
Pulses (beans)
Treenut
Groundnut
Soybean oil
Cotton seed oil
Tomatoes
Onions
Orange
Lemon
Grapefruit
Banana
Apple
Pineapple
Dates
Grape
Bovine meat
Pork meat
Poultry meat
Eggs
Milk
Butter

Water inputs per
kg prod (l/kg)

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

Fig. 1. Water productivity for energy in Kcal/m3 for California.

286

287

Fig. 2. Water productivity for protein in g/m3 for California.

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

288

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

Fig. 3. Water productivity for calcium in mg/m3 for California.

(1990) recommends that linoleic acid should provide about 2% of the total energy
and mentions that nutritionists suggest that an intake of fat providing 25±30% of the
energy is compatible with good health. As a whole in developed countries there is no
deficit in fat intake but rather it seems that fat intake is far too high in many developed
countries.
4.6. Vitamin A
Deficiency in Vitamin A is considered one of the major causes of malnutrition. It leads
to severe vision problems and blindness (Pellet, 1989) in hundreds of thousands of
children worldwide. Therefore, a systematic check of the Vitamin A content has been
made in all the investigated diets.
Vitamin A is measured in international units (IU) and the recommended daily intake
for adults is 4±5 kIU/day (kIU ˆ 1000 IU). Two major sources of Vitamin A are
vegetables, in particular carrots (280 kIU/kg), sweet potatoes (200 kIU/kg) and onions
(50 kIU/kg), and animal livers, ranking from 200 kIU/kg for poultry to 350 kIU/kg for
beef liver and 500 kIU/kg for lamb. The productivity of water for Vitamin A has been
analyzed only for significant products for which data were available. It shows that
productivity ranks from 26 to 49 kIU/m3, respectively for beef and poultry liver, to
340 kIU/m3 for onion and 1440 kIU/m3 for carrots.

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

289

4.7. Iron
Iron is vital for the production of hemoglobin, the vehicle for oxygen transport.
Deficiency in iron leads to anemia; women are much more sensitive to iron deficiency
than men. Leslie (1995) stated that iron deficiency is `the most widespread nutritional
problem among women.' As a consequence, the recommendations for iron are higher for
women (18 mg/day) than for men (10 mg/day).
An average of 15 mg/day has been considered as the requirement in this study. Iron is
found mostly in vegetables and in animal livers. Considering the water productivity for
iron, it was found that potatoes provided (57 mg/m3), vegetables (25±36 mg/m3); cereals
(20±30 mg/m3), liver poultry (20 mg/m3). These were the main iron sources and diets
optimized for the other factors were adjusted if necessary to reach at least the minimum
requirements.

5. Diets and water requirements
In this section we consider different diets and estimate the water requirements to
produce the corresponding food. As mentioned above estimates are based on California
crop yields and water productivity, and the diet reported for USA is considered as the
reference.
5.1. Diet 0: USA reference
The data used for the analysis correspond to the main components of the diet recorded
in USA for 1995 (FAO Balance Sheets, 1998). They include six animal products and 24
vegetal products. Sea and fish products, which contribute 6% of the protein availability,
and alcoholic beverages (beer, wine) which provide 6% of the total energy are not
included in the computation of water requirements.
As mentioned above, the FAO estimates of food availability discount for losses in the
storage, transportation, delivery and cooking. To estimate the carrying capacity of the
planet one needs to be aware of the difference between nutrition production from raw
product versus that realized by humans. However, the relative values and the relative
water savings that might be generated by a change of diet are instructive in guiding policy
changes.
Food intake per capita in USA categorized by food type and with the corresponding
relative water inputs are given in Table 4. The total water requirements to produce the
food is estimated to be 5.4 m3 per capita per day with nearly half required for meat
(46%). The reference values for nutrients per day (not considering sea, fish and alcoholic
products) are 3400 kcal of energy, 104 g of protein, 146 g of fat, 960 mg of calcium,
5 kIU of Vitamin A and 17 mg of iron. Unless specified otherwise, the water
requirements for each simulated diet presented below achieves at least the same values
as the reference diet for energy, protein, calcium, Vitamin A and iron. The fat intake is
allowed to fluctuate provided it is greater than the value recorded for Japan (80 g/day)
which has the lowest fat intake within the developed countries.

290

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

Table 4
Food intake for the reference Diet 0 corresponding to the food consumption in the USA in 1995
Product

Annual consumption (kg)

Fraction of water budget (%)

Vegetables
Fruits
Cereals
Sugar products
Milk eggs and butter
Oil
Meat

178
121
113
67
277
29
117

2
2.5
6.5
8
18
17
46

5.2. Diet 1: Animal products reduced by 25% and replaced by vegetal products
This scenario corresponds to a significant reduction of all animal products (milk-eggsmeat) by 25%, and their replacement by an increase in highly nutritious vegetal products.
The water required for this diet falls to 4.6 m3/day.
5.3. Diet 2: 50% beef replaced by poultry together with an adjustment of vegetal
products
In this scenario, poultry replaces 50% of the beef required for the protein and energy
needs. The water required for this diet is estimated to be 4.8 m3/day.
5.4. Diet 3: 50% red meat replaced by vegetal products
In this scenario, vegetal products (potatoes and groundnuts) replace 50% of red meat
(beef and pork). Sugar intake is slightly reduced to match the target level for energy. The
water required for this diet is estimated to be 4.4 m3/day.
5.5. Diet 4: Animal products reduced by 50% and replaced by vegetal products
This scenario corresponds to an important reduction of all animals products by 50%
and their replacement by highly nutritious vegetal products (potatoes, groundnuts and
onions). A further reduction of oil products is made to reduce the energy intake to the
target value. The water required for this diet is 3.4 m3/day.
5.6. Diet 5: Vegetarian
In this scenario, we consider a vegetarian diet, with suppression of all meat. Eggs and
butter components are maintained as in Diet 0. Milk is reduced to 70% of Diet 0. Balance
is obtained by increasing the highly nutritious vegetal products. The estimated water
requirement falls to 2.6 m3/day.

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

291

Table 5
Per capita productivity of water (reference to California)
Type of DIET

Water requirements
m3-day person

Increase in water productivity
from Diet 0 (%)

Diet
Diet
Diet
Diet
Diet
Diet
Diet

5.40
4.60
4.80
4.40
3.40
2.60
1.00

0
17
11
22
59
103
440

0
1
2
3
4
5
6

reference diet
25% reduction of animal product
Poultry replaces 50% beef
Vegetal products replaces 50% red meat
50% reduction of animal product
Vegetarian
Survival

5.7. Diet 6: Survival
This scenario explores an extreme diet, based only on the most productive products for
each nutrient considered. Only four products are necessary to achieve the targeted intakes
for energy, protein, fat, calcium and Vitamin A. They are potatoes, groundnut, onions and
carrots. The goal here is to bound the domain of water savings by defining an absolute
minimum water requirement given biological needs. For several reasons, this diet is not at
all realistic. It is certainly not sufficiently diverse or as nutrient rich as the other six considered. It also implies that large quantities of the same product would be consumed. This
would be quite difficult to implement. For example the quantities of potatoes and onions
per day are estimated to be 2 kg. However, further progresses in food processing can be
expected, and we cannot discard the possibility of future improvements in extracting
nutrients from current products. This diet requires a modest 1.0 m3 of water per day.
The above diets (1±6) define the range of water requirements for food and the water
savings that can be generated by a change in food consumption. It is somehow reassuring
to know that there is a high potential for water savings between the two opposite diets (0
and 6). Diet 0 is the rich diet whereas Diet 6 is the extreme opposite which still meets the
nutrition targets. Intermediate solutions include reducing some known excesses in current
diets such as a diminution of sugar and vegetable oil by 50% in Diet 0 will save 650 l per
day per capita. Daily water requirements per capita are summarized in Table 5 along with
the gain in water productivity resulting from a change in diet from Diet 0.

6. Nutritional water productivity and population
The challenge for feeding the population in the coming century is to find a balance
between the growth of the population, the evolution of diets and the likely availability of
water resources.
6.1. Population growth
Optimistically we assume it is more likely that the population will follow the lower
scenario of the well known United Nations projections for the year 2025 (from 7.6±9.4

292

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

billions). In the following we assume that world population will increase during the next
30 years by about 33% from 5.7 billions in 1995 (FAO data for year 1995) to some 7.60
billions in 2025. Population in developed countries was 1.29 billion in 1995 and is likely
to reach 1.45 billion in 2025. The remaining world population will increase from 4.4
billion in 1995 to 6.16 billion in 2025.
6.2. Diet changes
In the developed countries diets are rich or even excessive while in the developing
countries diets are fair or poor with sometimes important specific deficiencies, e.g. low
calcium intake. Various scenario of diets and intensiveness in the agricultural production
sector have been investigated on a regional basis by Penning de Vries et al. (1995).
They came to the conclusion that to relax the stress on food and on environment at the
horizon 2040, some changes in diets, i.e. less affluent, are desirable in many developed
countries.
Alleviating malnutrition in developing countries will require an increase in the food
intake. Furthermore, economic growth may also create an increase in the demand for
high-input food products as forecasted by Brown (1995) for China. Therefore, reducing
the wide gap between actual and maximum yields in developing countries is absolutely
crucial to meet the increase of the food supply requirements.
6.3. Water requirements
Using the same values of water productivity and yield for California, the daily per
capita water requirements in developed countries is estimated at 4 m3, in sharp contrast to
water requirements in developing countries of 1.3 m3. However, water productivity
recorded in California might not be appropriate for the developing countries where yield
and productivity are known to be lower. To take that effect into account we consider the
ratio of average yield for cereals in developing and in developed countries (2400 and
3300 kg/ha). If the ratio is applied, the water requirement for developing countries
increases from 1.3 to 1.8 m3 per day per capita.
The global water requirement estimate for 1995 is 13.1 billion m3/day (4790 km3/year)
and the projected need for 2025 is 16.9 billion m3/day (6190 km3/year). Without any
change in productivity and diets, the additional water needed to supply food is estimated
to be 3.8 billion m3/day (1400 km3/year), which represents an increase of 29% above
1995 requirements.
6.4. Global water demand and diet
Changes in developed countries diets from high-input to low-input foods might
significantly affect the world water balance. Table 6 contains estimates of water savings
and the contribution of these savings to meet the increases in global water demand by the
year 2025. Approximately 13% of the increase in water demand is met when poultry
replaces 50% of the beef meat and 81% is met for a change to the vegetarian diet, and
even more for the survival diet (not shown).

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

293

Table 6
Impact of diet change in developed countries on water availability in 2025
DIET in developed
countries in 2025

Water requirement
m3-day person
(reference Diet
0 ˆ 4.03)

Water savings
generated in 2025
Compare to dIET
0 billion m3/day
and in brackets
km3/year)

Percentage of the total
additional water
requirements for 2025
compare to 1995 (%)

Diet 1
25% reduction of animal product
Diet 2
Poultry replaces 50% beef
Diet 3
Vegetal products replaces 50% red meat
Diet 4
50% reduction of animal product
Diet 5
Vegetarian

3.45

0.85
(309)
0.50
(182)
0.88
(320)
1.5
(545)
3.10
(1130)

22

3.7
3.40
3.00
1.90

13
23
39
81

These estimates for the first time present a quantitative framework for a global
debate on water policy related to nutrition and population. How realistic are these
scenarios? For many social, political and religious reasons the vegetarian scenario may
not be desirable nor realistic. Substituting vegetables for 50% red meat and 50%
reduction of all animal product intakes, scenarios 3 and 4, respectively, seems to be more
practical in the long term. This generates a 23±39% of the additional water requirements
by 2025.
Its is noteworthy to acknowledge that some of the changes in diet are already under
way in developed countries. It is estimated that water requirements for food have dropped
between 1990 (4.4 m3/day/capita) and 1995 (4. m3/day/capita). This corresponded to a
global reduction in meat consumption and for a short period (5 years) a reduction of the
total intake; energy intake fell 4% and protein intake by 3%. Increasing awareness of the
relationship between health and diet played a central role. The consumption of meat in
the developed countries increased steadily to 78 kg/capita/year in 1990, more likely due
to the growth of income and productivity gains, but thereafter the trend reversed and the
latest data available (1996) shows a significant decrease to 72 kg/capita/year. The
downward trend for developed countries may continue.
The second change in diet is the replacement of beef and pork with poultry. Red meat
consumption peaked in the 1970s, and significantly decreased after 1990 as shown in
Fig. 4. For France, the break point started earlier in 1980. In developed countries, the
decrease of red meat is partially compensated by a continuing growth of poultry
consumption. Thus the current trend corresponds to a scenario similar to Diet 2, which
might ultimately generate 13% of the additional water requirements by 2025. Therefore,
it is realistic to think that greater awareness of consumers in developed countries of water
resource requirements to produce food, and also a more strict adherence to the real cost of
water might reinforce the current trend and lead to further savings.

294

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

Fig. 4. Evolution of meat consumption in developed countries (FAO Balance sheets).

The possibility of switching from one product to another is driven by site specific
agriculture conditions. It might be possible to convert some agriculture lands from forage
to cereals or vegetables for human consumption but impossible to convert mountain
pasture to a vegetable production system. Animal products and particularly milk are
essential particularly as a major source of calcium. In contrast confinement animal
agriculture for these contexts might not be appropriate and might even be harmful for the
environment in the long term.
The battle for water in the next century will be won on many fronts, such as improving
the efficiency and reliability of water delivery systems, minimizing non-beneficial water
use, optimizing the gap between actual and maximum yield, and, as suggested herein,
improving nutritional water productivity. The enormous advantages of water savings via
changes in diet are that production, medical, and environmental costs are reduced.
Therefore, it would be wise to promote water saving by increasing the awareness of
consumers of the true cost of water in food products.

Acknowledgements
The study owes much to F. Barthelemy (Ms.C student from ENGREF France in 1993)
who contributed to the earlier phases and developed the water consumption model for
crop and animal products. The authors are also thankful to David Seckler for his helpful
comments at various stages of the writing.

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

295

References
Bailey, R., 1990. Irrigated Crops and Their Management. Farming Press Books, Ipswich, UK, 192 pp.
Barthelemy, F.D., 1993. Water for a sustainable human nutrition: inputs and resources analysis in arid areas. MS
Thesis. Ecole Nationale du GeÂnie Rural, des Eaux et des ForeÃts, Stage de ®n d'eÂtudes, Paris, France, 120 pp
(unpubl.).
Brown, L.R., 1995. Who will feed China: Wake-up Call for a Small planet. W.W. Norton & Company. 163 pp.
BRL Memo d'irrigation, 1985. Technical lea¯ets for irrigation, Compagnie Nationale du Bas Rhone et du
Languedoc, 685 Route d'Arles BP 4001 Nimes France.
Carruthers, I.M., Rosegrant, W., Seckler, D., 1997. Irrigation and food security in the 21st century. Irrig.
Drainage Syst. 11, 83.
Chambers, R. 1985. Food and water as if poor people mattered: a professional revolution in water and water
policy in world food supplies. Proceedings of the Conference, Texas A & M University, College Station,
May 26±30.
DeTar, W., Browne, G.T., Phene, C.J., Sanden, B.L., 1996. Real-time irrigation scheduling of potatoes with
sprinkler and subsurface drip systems. In: Camp, C.R., Sadler, E.J., Yoder, R.E. (Eds.), Evapotranspiration
and Irrigation Scheduling, pp. 812±824. Proceedings of the International Conference, November 3±6, 1996,
San Antonio Convention Center, San Antonio, TX, St. Joseph, MI, ASAE.
Doorenbos, J., Kassam, A.H., 1979. Yield response to water. Food and Agriculture Organization, Irrigation and
Drainage Paper 33, Rome, Italy pp. 1±193.
Dunne, J.L., 1990. Nutrition Almanac, 3rd Edition. McGraw-Hill, New York, pp. 120±125.
FAO Balance Sheets. 1998. www.fao.org.
Feddes, R.A., 1988. Modeling and simulation in hydrologic systems related to agricultural development: state of
the art. Agric. Wat. Manage. 13, 235±248.
Gregory, P.J., 1991. Concepts of water use ef®ciency. In: Harris, H.C., Cooper, P.J.M., Pala, M. (Eds.), Soils and
Crop Management for Improved Water Use Ef®ciency in Rainfed Areas, pp. 9±20. Proceedings of an
International Workshop, May 15±19, 1989, Ankara, Turkey. Aleppo, Syria.
Islam, N., 1995. Population and Food in the Early Twenty-First Century: Meeting Future Food Demand of an
Increasing Population. International Food Policy Research Institute, Washington, DC, pp 1±239.
Leslie, J., 1995. Improving the nutrition of women in the third world, child growth and nutrition In: Andersen
et al. (Eds.), Developing Countries: Priorities For Action, Pinstrup. Cornell University Press, Ithaca, New
York, 1995, pp. 1±447.
Maozheng, Y., Wang, H., 1992. A study of water use ef®ciency of winter wheat in the north china plain. In:
Shalhevet, J., Liu, C., Xu, Y. (Eds.), Water Use Ef®ciency in Agriculture. Priel Publishers, Rehovot, Israel,
pp.1±297.
Molden, D., 1997. Accounting for water use and productivity, SWIM Part 1, International Water Management
Institute, Colombo, Sri Lanka.
Molden, D., Sakthivadivel, R., Perry, C.J., de Fraiture, C., Koezen, W.H., 1998. Indicators for comparing
performance of irrigated agricultural systems. Research Report 20. International Water Management
Institute, Colombo, Sri Lanka.
Pellet, P.L., 1989. Nutrition, health, and agricultural development. In: Clubb, D., Ligon, P.C., (Eds.), Food,
Hunger, and Agricultural Issues Nutrition, Health, and Agricultural Development. Winrock International
Institute for Agricultural Development, Morrilton, AR, 240 pp.
Penning de Vries, F.W.T., Van Keulen, H., Rabbinge, R., 1995. Natural resources and limits of food production
in 2040. In: Bouma, J. et al. (Eds.), Eco-regional Approaches For Sustainable Land Use and Food
Production. Kluwer, Dortrecht, The Netherlands, pp. 65±87.
Shalhevet, J., Liu, C., Xu, Y., (Eds.) 1992. Water use ef®ciency in agriculture. Proceedings of the
Binational China-Israel Workshop, Beijing, China, 22±26 April 1991 Priel Publishers, Rehovot, Israel,
297 pp.
Seckler, D., 1996. The new era of water resources management: from `dry' to `wet' water savings. Research
Report 1. International Water Management Institute, Colombo, Sri Lanka.
Stanhill, G., 1992. Water Use Ef®ciency. In: Shalhevet, J. et al. (Eds), Agriculture. Priel Publishers, Rehovot,
Israel, 1992, pp. 1±297.

296

D. Renault, W.W. Wallender / Agricultural Water Management 45 (2000) 275±296

Stone, J., 1975. Plant Modi®cation For More Ef®cient Water Use. Elsevier, Amsterdam, The Netherlands, 320
pp.
Sundar, A., Rao, P.S., 1984. Productivity and equity in irrigation tanks. In: Pant, N. (Ed.), Productivity and
Equity In Irrigation Systems. Ashish Publishing House, New Delhi, India, pp. 163±177.
Tinus, R.W., 1975. Impact of CO2 requirement on plant water use. In: Stone, J. (Ed.), Plant Modi®cation For
More Ef®cient Water Use. Elsevier, Amsterdam, The Netherlands pp. 1±320.
Young, C.A., Wallender, W.W., 1999. High resolution irrigation district hydrology balance: 1. water balance. J.
Irrig. Drain. Eng.