Since it takes 1,000 tons of water to produce 1 ton of grain, it is not surprising that 70 percent of world water use is devoted to irrigation. Thus, raising irrigation efficiency is central to raising water productivity overall.
...Any measures that raise crop yields on irrigated land also raise the productivity of irrigation water. For people consuming unhealthy amounts of livestock products, moving down the food chain reduces water use. In the United States, where the annual consumption of grain as food and feed averages some 800 kilograms (four fifths of a ton) per person, a modest reduction in the consumption of meat, milk, and eggs could easily cut grain use per person by 100 kilograms. For 300 million Americans, such a reduction would cut grain use by 30 million tons and the need for irrigation water by 30 billion tons.
Bringing water use down to the sustainable yield of aquifers and rivers worldwide involves a wide range of measures not only in agriculture but throughout the economy. The more obvious steps, in addition to more water-efficient irrigation practices and water-efficient crops, include adopting more water-efficient industrial processes and using both more water-efficient household appliances and those that use no water at all, such as the new odorless dry-compost toilets. Recycling urban water supplies is another obvious step in countries facing acute water shortages.
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