In a contest with implications for water agencies up and down California, voters in Marin County on Tuesday will decide between dueling ballot initiatives over a plan to turn seawater into drinking water.

Both measures require a public vote before the Marin Municipal Water District could build a 5-million-gallon-a-day desalination facility on the shoreline in San Rafael. But the measure proffered by a vocal group of desalination opponents bans the water agency from spending any money prior to construction, including funds for permitting, engineering and design work, unless voters approve it.

In effect, Measure T would stop the project in its tracks - a dangerous precedent in the water district's view, given the potential for drier, hotter years ahead due to climate change. The water district, the county's largest with 190,000 customers in central and southern Marin, relies on seven local reservoirs for three-quarters of its annual deliveries. Flows from the increasingly regulated Russian River supply the rest.

Data getting old

"It's a straitjacket," said Paul Helliker, district general manager. "Our cost estimates are now of a 2007 vintage. If we moved forward in two years the data would be five years old."

Measure S, the water agency's initiative, calls for a public vote before the first shovel plunges into the ground; but it differs from Measure T in that it lets the water district spend money to study the project. Helliker said additional permitting and planning work would cost $700,000.

Opponents suspect that figure is low, however, and say giving the utility free rein on planning amounts to writing a blank check on an already expensive project that has grave consequences for the environment. Most experts agree that reverse osmosis desalination, a process that pushes salt water through increasingly fine membranes, slurps up enormous amounts of energy. In addition, piles of brine - or the leftover salt - must be disposed of.

Building the facility would cost roughly $100 million; operating and financing it over three decades would add more than $300 million.

The district initiative "gives the MMWD Board more spending authority for more studies, plans and preparations for construction of their vastly expensive and monster energy-consuming desalination plant," the Marin United Taxpayers Association wrote in a recent newsletter.

Measure T backers

In addition to the taxpayers group, Measure T has support from Sustainable Fairfax, Sustainable San Anselmo and leadership of the three major parties in Marin County - Republicans, Democrats and Green Party. They contend the water district should first exhaust other options, including water conservation, recycling and the utilization of two emergency reservoirs.

"These are tough economic times," said Adam Scow of Food and Water Watch, which spearheads the anti-desalination movement in Marin. "Instead of exploring local efficiency programs and preventing water waste, the district is fighting us and trying to confuse people by putting their measure on the ballot."

Technically, the desalination facility was put on hold this spring after the water district found that water demand had dropped markedly. Still, over the long term, the Marin board and many other coastal water agencies expect to turn to the bay and ocean for drinking supplies. Two dozen water utilities from San Francisco to San Diego are examining desalination in some form.

If Measure T gains the required majority of votes (if both receive more than 50 percent, the measure with the largest number of votes prevails), some water managers worry it could have a chilling effect on desalination plants statewide. Supporting Measure S in Marin are the Marin Conservation League, the League of Women Voters, the San Rafael Chamber of Commerce, as well as the mayors of San Rafael, Ross, San Anselmo, Mill Valley and others.

Keep options open

"We need to keep our options open," said Tim Quinn, executive director at the Association of California Water Agencies in Sacramento. "That's extremely important for a lot of California water agencies right now."