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THE blizzards that hit the north-east US may have dominated the headlines last weekend, but across much of the country the is still biting 鈥� especially along the nation鈥檚 iconic waterways (see diagram).

Last week, lakes Michigan and Huron . In Illinois, the US Army Corps of Engineers has been on the riverbed in a bid to maintain the 3-metre depth that barges need to ferry exports to the coast.

Growing urban water demands have long clashed with the needs of agriculture and navigation, and climate change is expected to ratchet up the tension, causing wilder swings between drought and flood even in regions that may not get drier overall. Water shortages are only likely to intensify, setting states at one another鈥檚 throats. 鈥淭here isn鈥檛 and never will be enough water,鈥� says , a specialist in water-resources law at the University of Colorado, Boulder.

The US鈥檚 鈥渨ater wars鈥� are being fought in the courtroom, rather than on the battlefield (see 鈥�map鈥�), but only lawyers stand to gain if states and water districts sue to maximise their share of this precious resource. Can science and technology come to the rescue, in the form of 鈥渟mart鈥� water distribution and better modelling of supply and demand?

Previous big droughts of the 1930s and 50s saw conflicts settled by huge engineering projects like the on the border of Arizona and Nevada. Engineering solutions are still being considered in some places. Dredging the St Lawrence river to open shipping channels from the Great Lakes to the Atlantic has contributed to the lakes鈥� lowering levels, and now the , which manages waters shared by the US and Canada, is putting together a recommendation on how to improve things. This could include weirs and gates to control how much water drains away.

Elsewhere, budgetary constraints and concerns about the environmental impacts of big engineering projects have taken such options off the table. The stalled Lewis and Clark Regional Water System is a case in point. In 1989, leaders from 20 cities in Minnesota, Iowa and South Dakota proposed a system of pipelines that would draw water from the Missouri-Elk Point aquifer in South Dakota. Nine of the cities involved have little hope of ever getting the promised boost to their water supplies, now that federal funds, which covered 80 per cent of the $550-million price tag, . 鈥淲e have no way forward,鈥� says project director Troy Larson.

So states will have to produce better estimates of future supply and demand 鈥� and work out how to conserve what nature provides. Leading the way is the US Bureau of Reclamation鈥檚 , which has modelled a watershed that supplies some 40 million people across seven western states. It suggests an annual average .

Faced with numbers like that, finding ways to save water is a top priority. New techniques must go beyond asking people to water their lawns less frequently, and instead deploy smart delivery systems to cut wastage.

鈥淣ew water-saving methods must go beyond merely asking people to water their lawns less often鈥�

There are big opportunities to cut demand in agriculture. , a water engineer with the Bureau of Reclamation in Denver, is working on a project in Imperial valley, a former desert in southern California that has been turned into rich agricultural land. His simple goal is to turn off irrigation as soon as a field is fully watered.

To do this, a box is buried halfway across the field. Sensors detect when it fills with water and send a radio signal back to another unit that controls the flow, allowing the same amount of water to be applied again before automatically shutting off. Studies run with at the University of California鈥檚 Desert Research and Extension Center in Holtville show that the method reduces water use by about 10 per cent. 鈥淲e鈥檙e freeing up water through efficiency, rather than dams or pipelines,鈥� says Gill.

that there were about 12 million hectares of farmland across the US irrigated using the methods that Gill is improving. Achieving the same savings nationally could cut 1.5 per cent of the country鈥檚 total demand 鈥� but results will vary with soil type.

Gill is also working to prevent spillages in channels that move water around. The Maricopa-Stanfield Irrigation and Drainage District in Arizona recently replaced manual channel gates with motorised ones that are opened remotely before water backs up and spills out. It has cut its losses through spills from about 10 per cent to almost zero.

Cities are similarly starting to use smart distribution to cut their consumption. Charlotte, North Carolina, plans to reduce the amount of water its business district uses by 20 per cent over the next five years by giving building managers real-time information about their usage, using smart water meters with flow monitors.

Water use for cooling in power generation is another target for cuts. A indicated that switching the region鈥檚 power plants to air cooling could save 200 billion litres of water per year 鈥� 5 per cent of the shortfall predicted by 2060.

All of these approaches, and more, may be needed to avert shortages and costly legal battles. 鈥淭he cheapest water is going to be the water we can save, and we have a long way to go,鈥� says , an environmental lawyer at the University of New Mexico in Albuquerque.

This article appeared in print under the headline 鈥淲ater wars loom as US runs dry鈥�