A recent court ruling has spread a wave of concern for the local region's water supply. The ruling, made by a U.S. federal court judge last Friday, could lead to up to one-third less water being pumped from the Sacramento-San Joaquin Delta to cities in the Bay Area such as Pleasanton.

The pumping reduction stems from a court case initiated by the Natural Resources Defense Council regarding the protection of the Delta smelt, a 2- to 3-inch silver fish that once thrived in the Delta but is now dying off. The fish are being sucked through pumps such as those at a Tracy pumping station that distributes water to the East Bay and South Bay regions.

Officials at Zone 7, the water agency that wholesales water to 80 percent of Pleasanton residents as well as those in Livermore, Dublin and Dougherty Valley, are worried that the ruling will have a substantial impact on the local water supply. The agency gets 80 percent of its supply conveyed through the Delta by the State Water Project.

"We really could be in a bind if we're entering a drought or experience an earthquake that disrupts future water delivery," said Zone 7 General Manager Jill Duerig. "We may ask people to do more with less in order to protect our drought supplies and will be looking at additional tools and programs to help people do that."

The court ruling will cut up to one-third of combined State Water Project and Central Valley Project water deliveries for one year while state and federal agencies complete a long-term plan to protect the endangered fish, according to Zone 7.

Reserves of groundwater will help the water agency through next year, but Duergig said drawing down on those reserves could put the Valley in a "seriously vulnerable position" if dry weather conditions such as the ones this year, continue into a prolonged drought.

Last week's court ruling follows a nine-day period back in June where the Delta pumps were shut down to protect the smelt.

Some measures residents can take to reduce water usage include watering outdoors less, washing cars less frequently, repairing leaky sprinkler heads and household plumbing, turning off the tap while brushing teeth, taking shorter showers and running dishwashers and clothes washers only for full loads. More conservation tips are listed on Zone 7's Web site, www.zone7water.com.