|
E. Linacre |
4/'98 |
"Developing irrigation with the primary purpose of having it carry grazing interests over a drought period is economic nonsense." (1)
Clearly it takes much more water to sustain a meat diet, compared to a vegetarian diet. Therefore, the more limited water is, the more expensive meat will be in a market where water is unsubsideized.
Table 1: Amount of water (in liters or kilograms) required to produce the following commodities in Australia. The figures are approximate only and are higher in more arid areas, because of enhanced evaporative loss. From (2)
|
commodity |
Water (kg) |
|
1 kg of potatoes |
500 |
|
1 kg of maize |
600 |
|
1 kg of wheat |
850 |
|
1 kg of soybean |
1,900 |
|
1 kg of rice |
1,550 |
|
1 kg of cotton lint |
5,300 |
|
1 kg of cattle |
50,000 |
|
1 slice of white bread |
28 |
|
1 8-ounce steak |
4,660 |
A different comparison is in terms of the energy within the food, i.e. in terms of litres of water used per megajoule captured from the Sun. Potatoes and sugar cane need about 60 L/MJ, many fruits and vegetables entail about 180 L/MJ, and beef 2,500 L/MJ.
The amounts needed are much higher if the water is collected and delivered in an inefficient irrigation scheme. Often much less than 30% of the water stored in a dam is used by the plants; the rest is lost in storage and en route, chiefly by evaporation. That can be reduced by sub-surface irrigation, for instance.
References
(1) Meyer*, W.S. 1994. Smarter irrigation - an Australian perspective. Priv. communication.
(2) Meyer*, W. S. 1997. Water for food - the continuing debate. Priv. communication.
* Charles Sturt University, Wagga Wagga, New South Wales, Australia.