LIVERMORE -- In one of the Bay Area's harshest moves to save water, the Tri-Valley's water supplier agency is allocating only 75 percent of regular supplies to agencies that deliver tap water in Pleasanton, Livermore, Dublin and part of San Ramon.

Alameda County Zone 7 Water Agency, a wholesale water supplier, also is urging its four local water systems to adopt mandatory rationing and impose drought rates for some 200,000 people.

Zone 7 asked the public in late January to voluntarily cut water use 20 percent, but the savings amounted to only about half of that, officials said.

"After three dry years, we don't have the water to meet needs in regular years," Jill Duerig, the Zone 7 general manager, said Thursday.¿ "We have to do more to reduce water use."

Duerig sent out water cutback notices Wednesday to the local water systems: the cities of Pleasanton and Livermore, the Dublin San Ramon Services District and a private company that serves part of Livermore.

"We're telling them they will have to get by with 25 percent less water this year," Duerig said, "and it's up to them to figure out how to achieve that."

Among those to be cut, at least 25 percent are growers who raise wine grapes on about 3,500 acres in the Livermore Valley. Those growers could lose their water service entirely, however, if the state has no water in its South Bay Aqueduct, which delivers the untreated water directly to those vineyard owners.

Zone 7 is vulnerable to shortages because it relies on the State Water Project for 80 percent of its water in normal years, but the state is allocating nothing this year to the Tri-Valley agency.

There is some chance the State Water Project may increase allocations later this month due to late season rains, but state officials have said any increase won't be very much.

In a news release Thursday, Zone 7 Water Agency officials said the public will need to cut back outdoor water use by 50 to 60 percent if the area is to achieve an overall cutback of 25 percent.

Zone 7 asked the local water delivery agencies to ban wasteful practices such as watering during daylight hours, using hoses without shut-off nozzles, hosing off sidewalks and watering more than once a week in April and May.

Zone 7 will get through the year by drawing on water stored underground and in reservoirs.

The Dublin San Ramon Services District board is scheduled on Tuesday to consider water restrictions for its customers.

Contact Denis Cuff at 925-943-8267. Follow him at Twitter.com/deniscuff