ITHACA, N.Y. -- To save water, enter your ZIP code and click.

The Northeast Regional Climate Center (NRCC) at Cornell University has introduced a Lawn Watering Input Web site to make it easy for homeowners and groundskeepers to prevent lawns and grassy knolls from being saturated.

The site is at http://www.nrcc.cornell.edu/lawn_water .

Northeasterners who want to know if their lawns need watering can enter their ZIP code on the new Web site and click "submit" to get a fast answer.

Sprinkling a lawn every three days, whether it has rained or not, and using automatic timing systems wastes water, the climate center maintains.

Arthur T. DeGaetano, Cornell associate professor of meteorology, and Frank Rossi, Cornell assistant professor of horticulture, say that the soil can lose up to a half-inch of water for grass to remain viable. "People overwater their lawns," DeGaetano says. "Their lawns can remain green if homeowners stop relying on timing and focus on whether their lawns need watering or not. Lawns don't have to be constantly wet to stay green."

Keith Eggleston, senior climatologist at the NRCC, comments,: "If we had had a Web site last year, between May 20 and June 24 our recommendation for the New York City area would have been to abstain from watering lawns. "During the same period in 2002, our recommendation for greater New York would have been to water your lawn six times."

Behind the deceptively simple Web site is more than 2,000 lines of computer code, most of it written by Eggleston. The code uses the Penman-Monteith Evapotranspiration Model for soil-moisture predictions. The model considers air temperature, solar radiation, humidity, wind speed and the latest soil moisture readings.