The massive Rim Fire is closing in on Hetch Hetchy Reservoir in Yosemite National Park and is threatening the main water supply for the City of San Francisco and numerous other Bay Area communities. As of this morning, the fast-moving blaze was about 2.5 miles from Hetch Hetchy, according to a map created by the US Forest Service. If the enormous fire reaches the tinder-dry forests surrounding the reservoir, it could pollute the freshwater with huge amounts of ash. That’s bad news for San Franciscans and other communities that depend on Hetch Hetchy because the reservoir is not equipped with a water-filtration system.
“This fire is a tragedy,” said Spreck Rosekrans, of the environmental group Restore Hetch Hetchy, referring to a blaze that now covers more than 105,000 acres, or 164 square miles — roughly three times the size of Oakland. “And the water system is particularly vulnerable to the possibility of substantial amounts of ash getting into the water supply — because it’s unfiltered.”
San Francisco operates one of the few unfiltered water systems in the nation — and the only major one in California. That means that much of the water that flows out of people’s taps in the city comes straight from Hetch Hetchy without being filtered first. The San Francisco Public Utilities Commission, which operates Hetch Hetchy, has resisted building a filtration system because of the cost — at least $1 billion.
But without filtration, the city’s water supply, along with that of East Bay communities such as Hayward that buy water from Hetch Hetchy, is vulnerable to polluted stormwater runoff from major blazes like the Rim Fire.
The Rim Fire also could seriously damage San Francisco’s electric-power supply. O’Shaughnessy Dam at Hetch Hetchy provides hydroelectric power to the city and the huge fire has the potential to knock out major power lines.
Correction: The original version of this post erroneously stated that freshwater from Hetch Hetchy is also not treated. It is not filtered.