Sonoma and Marin county water agencies have begun urging customers to conserve water in the face of the worst drought the region has seen in at least a century.

The Sonoma County Water Agency and the nine municipal and regional water systems that use its water launched their first-ever wintertime conservation campaign on Wednesday with the theme "The Drought is On; Turn the Water Off."

Water managers say that Lake Sonoma, the centerpiece of the region's water supply, has about a year's worth of water left before the Water Agency would be forced to ration the supply to client cities and districts and their 600,000 customers. Coming out of a record dry year in 2013, they are hoping to extend that Lake Sonoma supply as long as possible before it reaches a critical level.

"We're very concerned; we want to take a proactive approach .<TH>.<TH>. The more we can do now, the less dire an impact it will have on us if this continues," said David Guhin, utilities director for the city of Santa Rosa, the largest water system reliant on Lake Sonoma.

The campaign will feature ads online in local broadcast and print outlets urging residents to conserve water, cutting down landscape irrigation, car washing, and other outdoor activities and publicizing existing programs to replace indoor appliances and fixtures with more efficient models.

This builds on an earlier campaign, over the summer, urging residents to take the "20 gallon challenge," reducing their usage by that much every day. This new call, however, is much more urgent given the dire lack of precipitation in the rainy season so far.

Santa Rosa ended 2013 with just 8.71 inches of rain, according to Press Democrat records. The normal rainfall is 32.22 inches. According to Water Agency data, last year was the driest in 119 years of record keeping, well below the severe drought years of 1976 and 1932.

Water levels have fallen so low in Lake Mendocino near Ukiah that the Water Agency has received state permission to slash flows into the upper Russian River to preserve what little is left for next summer. That is forcing cities north of Dry Creek, which are upstream of Lake Sonoma and thus cannot draw water from Lake Sonoma, to make plans for mandatory water conservation; the Mendocino County Board of Supervisors cleared the way for those measures Tuesday by declaring a "drought emergency."

In Napa County, reservoirs also are dwindling and the cities are eyeing their allocations from the State Water Project nervously. State water managers have warned that they will be able deliver as little as 5 percent of the normal allocation from the huge network of reservoirs that supplies much of Northern and Central California, though not Sonoma and Mendocino counties.

Forecasters say there is a glimmer of hope for later this year, with some early signs that warming water in the Pacific may generate the condition known as "El Ni?" that normally means wetter weather on the West Coast.

In the short term, however, the North Coast has little prospect of rain. The National Weather Service said Wednesday that a weak weather system will move into the Pacific Northwest over the next few days, bringing a dusting of snow to the Sierras and rain to the upper Sacramento Valley as early as Saturday, but that is unlikely to generate much precipitation in the North Bay.

The winter-time conservation campaign is intended to save water now and get customers accustomed to drought conditions going into the summer, when demand peaks and Lake Sonoma will be under the most strain should the winter remain dry, said Grant Davis, general manager of the water agency.

The worst case scenario, he said, would be to see water levels drop so low that the cities can't get the water they need and flows in the river falls so low to damage habitat for wildlife. "And that is a real possibility ... we have to plan for that," he said.

Water managers say existing conservation efforts, including subsidizing water-efficient home fixtures, programs developed in the wake of droughts in the '70s and '80s, already have led to a dramatic reduction in regional water consumption, despite a surging population. Guhin said the city estimates the efficiency measures save about 1.4 billion gallons per year in Santa Rosa's system alone.

But residential demand accounts for about three-quarters of all water use in Santa Rosa, with the rest being for commercial and industrial users. The city, hoping to replicate the sucess in residential conservation on the commercial side, hired a consultant late last year to do "water audits" for businesses and help owners use water more efficiently.

The municipal water systems and regional districts participating in the campaign are the cities of Cotati, Petaluma, Rohnert Park, Santa Rosa, Sonoma, Windsor, and the North Marin, Valley of the Moon, and Marin Municipal Water Districts.

"We hope this campaign will create a buzz in the local coffee shops and get our community to not only talk about saving water, but take action by following some easy water saving tips," said Jake Mackenzie, Rohnert Park city council member, in a release announcing the campaign. "Every drop of water matters at this point."

Information on the drought situation and tips for conserving water are available at wateroff.org.

You can reach Staff Writer Sean Scully at 521-5313 or sean.scully@pressdemocrat.com. On Twitter @BeerCountry.