As a special report on water in the Economist (May 20, 2010) said, "In truth, though, such water is not all lost: much of it returns to the aquifers below, from where it can be pumped up again. There is a cost to this, in energy and therefore cash, but not in water. The only water truly lost in a hydrologic system is through evapotranspiration (ET), since no one can make further use of it once it is in the atmosphere."

If genuine savings are to be made, measures should be taken to cut non-beneficial ET or reduce ET (for example, by reducing irrigated areas or producing food with less transpiration). Growing more crops over a wider irrigated area or increasing of cropping intensity in the same area raises the level of ET.

In many water-scarce areas in the world that are similar to North China, policies aimed at reducing the use or drawing of water have actually increased groundwater depletion. This has happened in the Upper Rio Grande basin shared by the United States and Mexico, where measures designed to make irrigation more efficient have increased crop yields upstream, which in turn have raised the level of ET and left less water to replenish aquifers.

Such facts increase the attractiveness of demand management that is being tried in China. In irrigation projects that cover several parts of arid and semi-arid areas, including Water Conservation Project, GEF Hai Basin Integrated Water and Environment Management Project and the Xinjiang Turpan Water Conservation Project, the World Bank has been promoting water conservation with focus on reducing consumptive use of water or ET.

As part of the Water Conservation Project, farmers have formed water-users' associations to plan and operate irrigation services. But the objective is specifically to reduce consumptive use of water or ET and simultaneously increase the farmers' incomes (for example, by using integrated engineering, and agricultural and management measures such as crop pattern adjustments) without further depleting the groundwater table. The objective is also to increase the yield and value of production per unit of ET and stay within the fixed consumption quota.

According to project monitoring data, the farmers' per capita income increased by 193 percent and water productivity rose by 82 percent, while consumptive use of water or ET over the irrigated areas fell by 27 percent by the end of the Water Conservation Project (2000-2006), which was financed by the World Bank and implemented by the Ministry of Water Resources. The project shows that the main strategic goal of combating water scarcity is to find better ways to reduce the consumptive use of water or ET, and increase farmers' incomes in addition to many other good measures.

The author is a senior irrigation specialist at World Bank.