Local cities are searching near and far for water, hoping to cobble together a large enough supply for Napa Valley residents to survive a third dry year.

As things stand, American Canyon and St. Helena are contemplating mandatory conservation measures, while Calistoga will consider voluntary cutbacks.

Napa and Yountville are the valley’s two most water-affluent cities, with no special conservation measures in the offing.

Felix Riesenberg, the county’s principal water resources engineer, gave this assessment to the Napa County Flood Control District’s board of directors on Tuesday.

Despite a dismally dry December and January — traditionally, two of the wettest months — Riesenberg said it was too early to panic. “It’s part of our job not to come out and say ‘The sky is falling’ until it is falling,” he said.

Napa is in the best position, with likely access to 28,720 acre feet, but an estimated 2009 demand of only 15,500 acre feet, he said.

“They have a very aggressive water conservation program,” Riesenberg said. “They’ve set themselves up to be in good shape.”

Despite a decade of substantial growth, Napa used the same amount of water in 2007 that it consumed in 1997, Mayor Jill Techel, a flood board member, said.

Napa is relying on its two local reservoirs for 22,000 acre feet, while tapping five sources outside the county for some 7,000 acre feet, Riesenberg said. The city’s goal is to use outside sources first, keeping as much local water as possible in reserve for 2010.

Yountville, which uses 600 acre feet per year, expects to have no trouble obtaining that amount from state-owned Rector Reservoir, Riesenberg said.

St. Helena has the greatest shortage. Residents would be expected to consume 2,000 acre feet this year, but only 1,500 acre feet are available, Riesenberg said.

The St. Helena City Council intends to declare a water emergency, allowing the city to impose mandatory conservation measures, including limits on outdoor irrigation.

American Canyon would be expected to use 3,080 acre feet this year, which closely matches a potential supply of 3,090 acre feet, Riesenberg said.

But several of American Canyon’s sources are iffy, requiring special purchases and abundant flows through the Sacramento Delta this spring, Riesenberg said.

For this reason, the American Canyon City Council set in motion on Tuesday steps leading to a mandatory conservation ordinance to reduce consumption.

Calistoga has access to 765 acre feet, but could be expected to consume 800 to 820 acre feet, Riesenberg said.

Mayor Jack Gingles, who sits on the flood board, said he would propose that the Calistoga council adopt voluntary cutbacks. “It just seems we should be more concerned than we are,” he said.

A key component of every city’s water supply, except St. Helena, is the State Water Project, which is projecting deliveries of just 15 percent of contract amounts this year.

This could rise if the spring is a wet one, but it could potentially fall if dry conditions persist, Riesenberg said.

The weather pattern for Northern California may be changing, with back-to-back storms predicted for today and Friday, forecasters report.