UNIVERSITY PARK, Pa. -- During a drought, it may be tempting to give the lawn a daily sprinkling, water the vegetable garden for an hour each morning or start irrigating your 300 acres of corn. Before you do, take note of how much water you will use consumptively.

"Consumptive use of water occurs when water is drawn from a ground or surface source and not directly returned to the earth," explains Al Jarrett, professor of agricultural engineering in Penn State's College of Agricultural Sciences. "It's a major concern during drought emergencies."

Consumptively used water doesn't disappear forever. It is released into the atmosphere through evaporation and transpiration. But it can be reused only when it returns to the earth as precipitation -- and in a dry summer, that could take a while.

The water you sprinkle on your lawn and garden is used consumptively since it either evaporates or is taken up by the plants' roots. So are the 9,000 gallons of water taken from the soil by an acre of corn on a hot July day.

The 3.5 gallons of water used to flush the toilet or the 30 gallons used to wash a load of clothes is not used consumptively since it returns to the earth once it is treated. A dairy cow can drink 20 gallons of water in a day, but only half is used consumptively in milk production. The rest returns to the earth as waste.

"Not surprisingly, agriculture is one of the largest consumptive users of water," says Jarrett. "It requires an average 600,000 gallons of water each year to grow an acre of any crop. Except for the small amount that remains in the stems and leaves, all of this water is transpired into the air."

During a declared drought emergency, there are limitations on the amount of water farmers may use consumptively. In the Susquehanna River Basin, the limit is an average of 20,000 gallons per day. In other areas, certain water uses may be restricted.

Homeowners watering lawns and gardens also should monitor water consumption during a drought. Garden hoses, sprinklers and basin faucets use from three to five gallons per minute. If you run a sprinkler for two hours, that can amount to 600 gallons.

During a drought emergency, you should contact the river basin commission in your area if your water use is more than 20,000 gallons of water a day, or if you are considering a large irrigation project. The commission regulates water use and can assist with planning large water-use projects.

If you are located in the Susquehanna River Basin, contact the Susquehanna River Basin Commission, 1721 North Front Street, Harrisburg, PA 17102, (717) 238-0427. Growers in the Delaware River Basin can contact the Delaware River Basin Commission, P.O. Box 7360, West Trenton, NJ 08628, (609) 883-9500.

For further information or for a listing of fact sheets on water consumption and other issues, contact the Agricultural and Biological Engineering Department, 246 Agricultural Engineering Building, University Park, PA 16802, 814-865-7685.

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EDITORS: For more information, contact Al Jarrett at 814-865-5661.

Contacts: John Wall jtw3@psu.edu 814-863-2719 814-865-1068 fax