Christina O'Haver, The Union Democrat

San Francisco voters will take the first step in determining the fate of the Hetch Hetchy Reservoir in Yosemite National Park and whether city residents will have to find alternate sources of water in a measure to be voted on next week.

If passed, Proposition F would require the City and County of San Francisco to develop a plan to drain the Hetch Hetchy Reservoir, and identify alternative local water and renewable energy sources.

The city would spend up to $8 million to devise the plan, and aim to complete it by 2014 so that a charter amendment calling for the actual removal of the reservoir could be placed before voters in 2016.

Proponents of the measure hope to restore Hetch Hetchy Valley close to its former state, before the reservoir and O'Shaughnessy Dam were built in 1923.

"In order to restore Hetch Hetchy Valley, you have to move the reservoir," said Mike Marshall, executive director of Restore Hetch Hetchy, which backs Proposition F.

Opponents are concerned about future water supply for 2.6 million Bay Area residents who receive drinking water from the Hetch Hetchy Reservoir. According to the San Francisco Public Utilities Commission, which operates the reservoir, Hetch Hetchy stores about 85 percent of water delivered to the city.

PJ Johnston, spokesman for Save Hetch Hetchy, which opposes Proposition F, said in dry years, it stores closer to 100 percent of the city's water.

Johnston said other parts of California would feel the effects if the reservoir was drained because of the constant statewide battles over water.

"It's worth remembering that the entire state of California fights over water," he said. "There's not enough of it to go around."

Restore Hetch Hetchy argued that the reservoir is one of nine that comprise the San Francisco Public Utilities Commission's water system. The city rebutted that only six of the reservoirs hold drinking water and Hetch Hetchy stores 117 billion gallons - 42.7 billion more gallons than the other five combined.

Opponents also argue that draining the reservoir would be a costly process.

Save Hetch Hetchy estimates that moving the reservoir would cost as much as $10 billion. The San Francisco Public Utilities Commission said the $8 million proposed for drawing up the plan would be insufficient.

"It's been studied to death and it's come back a bad idea every time," Johnston said.

However, proponents say draining Hetch Hetchy Reservoir could attract more tourists to Yosemite National Park by offering them a "second Yosemite Valley."

Jerry Cadagan, a Sonora resident who served on the Restore Hetch Hetchy board for several years, said it could be an economic boost for Tuolumne County.

Cadagan said restoration could either be passive - drained and left alone to restore itself - or assisted by human efforts. If people visit the park to assist in restoration efforts, they would likely patronize businesses in the area, he said.

Cadagan supports draining the reservoir but believes the O'Shaughnessy Dam should be left in place as a reminder of "our selfishness and stupidity" for allowing it to be built a century ago.

He said tearing down the dam could pose environmental problems and it would only be an eyesore for part of the Hetch Hetchy Valley, which would be several miles long.

Although the decision is in the hands of San Francisco voters, Cadagan believes many people in Tuolumne County would support the draining of the reservoir because the county has lost control of much of its water to outsiders.