As of this morning, the wildfire near Yosemite had grown to 250 square miles and reached as close as 20 miles to the Yosemite Valley. The fire was only 15% contained. In addition to threatening the park, the fire also is close—half a mile—to the Hetch Hetchy reservoir, which supplies 85% of the water used in San Francisco. Although the water supply is currently safe, according to the SFPUC, a lot of San Franciscans are understandably fretting. Are their worries justified? What would happen if Hetch Hetchy were to go down?
Hetch Hetchy supplies 265 million gallons per day—more than enough to meet our demand of 94.9 million gallons per day, according to the SFPUC's 5-year report. (The rest of the supply either goes to other cities in the Bay Area or is stored in reservoirs.) That number ignores groundwater uses, like watering a golf course in Sunol, or out of city users like Lawrence Livermore National Laboratory.
Here's the good news: Even if Hetch Hetchy were out of commission, we have five years' worth of water stored in various reservoirs in the mountains, the East Bay Area, and the Peninsula. We have two other reservoirs up-country—Lake Lloyd and Lake Eleanor—that hold a combined 98 billion gallons. Those alone would last us about 1,000 days—three years—which would be more than enough time to repair Hetch Hetchy or to devise a long-term workaround.
But what if we were to be cut off from our entire Sierra Nevada water catchment? Well, then we're in a little more trouble. That's because we keep 48 billion gallons in reservoirs in the East Bay and 7 billion on the Peninsula. Combined, those supplies would keep us for about 800 days. And, of course, if we had access to both sets of reservoirs, both in the mountains and locally, we'd be looking at maybe five years of water. Nothing to worry about.
Except, what if we lost—say by earthquake—our access to all water outside of the City? We're supplied by four pipelines that come up through the Peninsula—what would happen if we lost those?
In that case, things don't look good. We keep only 413 million gallons in reservoirs here in the City, and have only minimal capacity to generate our own water. Our supply wouldn't be able to meet normal demand for more than four days. The PUC's goal is to restore basic service within 24 hours of an earthquake. But even with reduced consumption during an emergency, there's not a huge margin of error.
So how much water should you keep in your emergency kit? (You do have an emergency kit, don't you?) According to FEMA, normal water consumption is about a half a gallon per day, plus another half gallon for food prep and hygiene. So you should be looking at one gallon per person per day. The City of San Francisco recommends a three-day supply—so three gallons per person.
In the case of a water emergency, the SFPUC has made plans, including the designation of 67 emergency fire hydrants, the creation of a water disinfection station at the Zoo's well, a supply of emergency water bladders and bagging machines, and coordination with other jurisdictions to bring in supplies.
So, all in all, the picture isn't as bleak as some are painting it. But it might not be a bad idea to stock up on some five-gallon jugs anyway.