But the use of more corn to make ethanol could drain water supplies like the Ogallala, or High Plains, aquifer, which extends from west Texas up into South Dakota and Wyoming.

"The aquifer is already being mined to the extent that recharge of precipitation into it is much, much less than withdrawals, and that would be exacerbated by any increase in corn or any increase in irrigated agriculture in the region," Jerald Schnoor, a professor of environmental engineering at the University of Iowa, told reporters on a conference call about the report. Schnoor chaired a committee set up to develop the report.

Large portions of Ogallala show water declines of more than 100 feet (30 m), said the report from the Council, which advises Congress and the federal government on scientific matters.

Corn requires more irrigation than other crops like soybeans and cotton in the Plains states across the middle of the country, the report said. Much of the water used to irrigate corn, the main source of ethanol in the United States, is lost to the ecosystem as it evaporates from the plant and from the ground.

DEAD ZONES

Schnoor said poor water supplies in some parts of the US Midwest have already stopped a few ethanol refineries, also heavy water users, from being built in Iowa and Minnesota. If they had been built, water supplies to a few towns there may have suffered, he said.

In addition, fertilizers used to produce corn could increase the runoff of oxygen-starving nitrogen into streams that run down the Mississippi River into the Gulf of Mexico. Such runoff has been blamed for forming "dead zones" in the Gulf where many forms of marine life cannot survive.

Schnoor said each gallon of ethanol made from corn can leave behind about 8 grams, or about the weight of three pennies, of nitrogen that can wind up in water supplies.

A similar report from nonprofit group Environmental Defense this summer said ethanol could increase demand for scarce water supplies by 2 billion gallons a year.

Ethanol industry sources have said concerns about ethanol's impact on water supplies are overblown and that ethanol plants will not be locating where water availability is a question.