On the face of it, it's pretty simple for people like famous Hollywood actors, billionaire "enviro-barons" sitting in Little Rock, Ark., or even the editors of The Bee to support Proposition F, a local ballot measure in San Francisco that calls for the destruction of Hetch Hetchy Reservoir.

After all, none of them rely on Hetch Hetchy for their drinking water.

But 2.6 million Bay Area residents do. Some 30 Bay Area cities across four counties rely on Hetch Hetchy water, not just the city of San Francisco that proponents like to focus on.

Yes, the creation of the Hetch Hetchy Reservoir, a century ago, was John Muir's last great, failed battle.

No, most of us would not choose to build the reservoir in the same place, next to Yosemite Valley, if we were making the decision in, say, 2013.

But that decision was made in 1913.

And in the century since, the Hetch Hetchy Water & Power System has delivered 220 million gallons of pristine water each day, and 1.7 billion kilowatt hours of carbon-free hydroelectric power each year, to a Bay Area that largely wouldn't exist had Hetch Hetchy never been built.

And while the movement of water across the state is the single-greatest consumer of electricity in California, Hetch Hetchy stands as the exception -- a marvel of sustainable engineering, decades ahead of its time, which delivers all this water and power via gravity.

Still, some argue, the reservoir is an abomination, and the valley should be restored -- the Bay Area be-damned.

Well, be careful what you ask for.

The Department of Water Resources estimated the cost of this decision to be between $3 billion and $10 billion. Who would pay these billions? Well, at every stop along the campaign trail in San Francisco, Prop. F's Mike Marshall acknowledges that San Francisco can't foot that bill ... and says the state of California and the federal government will have to pay.

Hard to imagine that the state and the federal governments have huge appetites for spending billions to eliminate water storage, decrease water security, and increase CO2 pollution.

Frankly, the backers of Prop. F have their priorities out of whack. Imagine the good $10 billion could be put to:

• We could fully fund our statewide water infrastructure deficit.

• We could triple the entire U.S. parks budget.

• We could pay for every single California high school graduate to attend the University of California for two years.

Or, as Prop. F's backers would have us do, we could spend that money tearing down the lynchpin of a clean and reliable water and power system that millions of Californians rely on.

And look-out: studies have shown that there are no financially feasible alternatives for storing that water, meaning the Bay Area would face water shortages in one out of every five years.

How long do you think it'll take before San Francisco's Hetch Hetchy-dependent neighbors demand their full allocations from the Delta, fighting along with everybody else for its scarce water?

The environmental cost could be huge as well. According to an estimate in the Earth Island Journal, the loss of Hetch Hetchy's hydroelectric power could lead to 387,000 tons in increased carbon emissions each year.

So instead of developing wind, solar and other green power sources to expand our sustainable energy portfolio and fight global warming -- as the city does with the largest municipal solar installations in the state, which are funded through the sales of clean Hetch Hetchy power -- eliminating Hetch Hetchy would force San Francisco to find billions just to replace the clean water and power it has now.

These are the reasons -- not the rank provincialism that distant observers like to suggest -- why every elected official and community organization in the Bay Area opposes Prop. F.

Finally, Marshall and other critics, notably The Bee, like to scoff at San Francisco's environmental record, pointing out that conservative Orange County leads the state in water recycling, and that liberal San Francisco is lagging far behind.

Well, San Francisco is the state leader in water conservation - using less than half the state's per capita average, about one-third that of both Orange County and Sacramento - together the worst in the state.

But fair enough, San Francisco should do more water recycling. Which is why the city has already begun implementing a very real water recycling program, costing tens of millions of dollars, all paid for by - you guessed it - Hetch Hetchy Water & Power.

San Francisco will begin its newest recycled water project on the city's west side. It cost about $9 million. We'd like to continue spending our money on real solutions like this, rather than pipedreams that could lead to real nightmares.

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