The great water myth

In a world of growing water shortages, farmers are becoming convinced that they need to grow, "more crops for every drop." Water efficiency is all the rage in an industry that uses two-thirds of the world's water. But could the farmers be wrong?

From the corn fields of Mexico to the paddy fields of China to the lettuce plantations of California, farmers are discovering that a few simple inexpensive techniques, such as lining irrigation canals to prevent leaks and delivering water directly to plant roots rather than flood fields, could cut world water use by a quarter or more.

The World Bank and aid agencies are pouring money into water efficiency. The water saved is being earmarked for growing more crops; for refilling empty rivers; and even for resolving international disputes. It could solve the US's current dispute with Mexico for not delivering all the water to Texas which was promised under a 1944 water-sharing treaty.

And yet one of the World Bank's chief advisers on water, Stephen Foster of the British Geological Survey, is horrified by the idea that making irrigation more efficient will free water for other uses. "It has the makings of a very dangerous myth," he says.

There is, he adds, a horrible flaw in the argument. Most of the water being "saved" is never truly wasted in the first place. Some, it is true, is lost to evaporation. But most - the water that seeps underground from fields and canals - eventually finds its way to nature's underground water reservoirs, from which millions of farmers subsequently pump water to supplement river water for irrigation.

This water is not being wasted at all, merely put into store; "saving" it will simply empty the water store. The repercussions, says Foster, could spell hydrological catastrophe in countries such as Mexico and India that rely increasingly on underground water for irrigation.

Andrew Keller of the International Water Management Institute, a World Bank-backed research body, agrees. In a recent paper, he argued that, "the classical concept of irrigation efficiency can lead to serious mismanagement of scarce water resources, because it ignores the potential re-use of irrigation return flows."

And that is what seems to be happening on the banks of the Rio Grande, on the border between Texas and the Mexican state of Chihuahua. After more than a decade of drought, this is a region desperately short of water. And the river is failing. In its middle stretches, downstream of El Paso, the Rio Grande is virtually empty. All the water has been taken by cities and farmers upstream, where the river is entirely within the US. The river only recovers a little when a new tributary, the Rio Conchos, arrives from Mexico bringing a small but significant flow.

Well done to the Mexicans, you might say. But Texas is not so charitable, for the Mexicans are in default of a treaty signed 60 years ago with the US to share the river's flow. Come drought or flood, the Mexicans are required to deliver at least 350,000 acre-feet of water to the border. But for the past decade of drought, as their own reservoirs have emptied, the Mexicans have not delivered enough. They are now four years behind with their water deliveries.

Texas farmers are angry, but Mexican farmers shrug their shoulders. "We have no water to give," one told me. "How can we give the Texans what we don't have ourselves?" But unless they make good soon, the US administration has threatened hydrological retribution by stopping flows down the other cross-border river, the Colorado, into Mexico.

Water engineers along the border hope they can stave off a water war. The Border Environment Cooperation Commission (Becc), a cross-border body set up under the Nafta free trade agreement, is investing in water-saving measures on Mexican farms in order to help them meet their treaty obligations.

This summer, engineers are lining the canals on the largest irrigated area, at Delicias, which waters fields of alfalfa, pecan and tomatoes for 90 miles along the River Conchos. And proud farmers there show off the perforated hoses they now run across their fields to deliver water where once they simply flooded the fields.

The plan is to halve the water use in the Delicias irrigation district. "The Americans will get what we save," says Marcial Marquez, chairman of the irrigation district. That, says Gonzalo Bravo of the Becc, "will be nearly equal to the amount of water Mexico is required to send to the US under its treaty obligations."

It sounds like a win-win situation, until you remember that farmers here also use a large amount of underground water to keep their crops growing, especially during the drought. The worry is that with less water allowed to percolate from fields into the underground reserves, those reserves will soon begin to falter.

The Delicias irrigation operations manager Ezequiel Bueno told me he had no such fears. So far, he explained, there are only sporadic signs of falling water tables. But local researchers I spoke to are worried and tell a very different tale.

"Some people think groundwater comes from Mars and surface water comes from Venus. They just don't realise how connected they are," says Hector Arias of the conservation group WWF, which has a project to help save the rivers of the Chihuahua desert. The tragedy is that, to meet their immediate treaty requirements for delivering water to Texas farmers, the Mexicans are imperilling the long-term future of their own underground water reserves. This story, albeit without the troubles of cross-border antagonism, is being played out in different forms across the world, as farmers pump ever more water from their underground water reserves while starving those reserves of the water they need to refill.

So what should happen down on the desert borderlands between the US and Mexico? Arias says that water managers need a better understanding of both the water cycle and the sheer scarcity of water.

Some farmers are taking the hint and giving up. Terry Bishop at Presidio in Texas is negotiating a deal that will allow him to sell his share of Rio Grande water - allocated to his land 80 years ago - to thirsty cities downstream such as Laredo. He would like to carry on farming, on what he believes is one of the longest continually cultivated stretches of land in the US. But, "the water is too valuable to stay here," he says.

Just over the border from Presidio in Ojinaga, where huge areas of irrigated farms have been abandoned to the desert in the past decade for want of water, the Mexican agriculturalist Humberto Lujan has another idea. He says the future lies in new crops that need less water. Why not grow ornamental cactuses, he says, or herbs such as rosemary, or mesquite, a desert shrub that provides both good timber and cattle fodder with very low water needs?

Lujan has planted a patch of abandoned farmland with these crops to show how it can be done. If the scheme succeeds, he says, he may not be producing more crops per drop - but he will certainly be earning more dollars.