SANTA ROSA -- Sonoma officials Thursday took concerns over their water woes a step further than their Bay Area neighbors by ordering mandatory -- not voluntary -- rationing for the more than 600,000 people who use their service.

The Sonoma County Water Agency said it had little choice but to install the rationing requirements after the state ordered them to cut back on water diversions from the Russian River by 15 percent to protect salmon.

Sonoma joins Santa Cruz as the only Bay Area counties that have resorted to mandatory rationing.

Santa Cruz officials ordered rationing by their customers in May. The restrictions are light, concerning only residential irrigation, according to Santa Cruz Water Conservation Manager Toby Goddard.

Residents are prohibited from watering their lawns and gardens between 10 a.m. and 5 p.m., seven days a week.

Warnings will be issued to water abusers. For those bold enough to ignore a warning received in person, a $60 citation could follow. If the citation doesn't change behavior, overzealous water users could have their water supply turned off, according to Goddard.

Professional gardeners, and people employing drip systems and shut-off nozzles are exempt from the ban. Watering by hand was also permitted.

"Keep water on the plants and not running down gutters,'' Goddard said.

While Sonoma and Santa Cruz water officials were forced to order rationing, other Bay Area agencies were relying on voluntary cutbacks by their utility customers.

The San Francisco Public Utilities Commission reported on Tuesday that water consumption among counties served by the Hetch Hetchy regional water delivery system was down 11 percent.

The announcement came just two months after the commission called for voluntary water conservation efforts among its Bay Area customers following one of the driest winters on record.

Customers in every part of the service area - San Francisco, the South Bay and the East Bay - showed a reduction in demand over a normal year, according to the commission.

The commission serves 2.4 million customers in San Francisco, San Mateo, Santa Clara and Alameda counties.

Meanwhile in the South Bay, the massive Santa Clara Valley Water District was urging county residents and businesses to voluntarily cut back their water use by 10 percent.

"Because of a prolonged dry winter and sudden reduction in water supply from the Delta, our reserves are being depleted at a faster rate than anticipated," said Tony Estremera, chairman of the water district board of directors.

The Sacramento-San Joaquin River Delta delivers about half the county's water supply.

The Santa Clara Valley Water District manages wholesale drinking water resources and provides stewardship for the county's five watersheds, including 10 reservoirs, more than 800 miles of streams and groundwater basins.