Recycled Water Study Shows SF Will Still Need Hetch Hetchy

Hetch Hetchy Resevior in Yosemite National Park, the source for much of San Francisco's water. Photo by Flickr user melfoody.

This November, San Francisco’s Prop. F asks voters to approve an $8 million planning process to find a way to drain Hetch Hetchy Reservoir, the city’s most important water system asset. SPUR believes that this is a bad idea for many reasons, and we strongly oppose Prop F (stay tuned at for our full ballot analysis in early October).

The measure also calls for a task force to develop a long-term plan to improve water quality and reliability, and to identify new local water sources to supplement water currently diverted from the Tuolumne River into the Hetch Hetchy system. As we have said before, it is so obviously a good idea to plan for alternative supplies that such endeavors are already well underway in San Francisco (and we certainly don’t need a ballot measure to compel us to do planning that is already being done). The San Francisco Public Utilities Commission (SFPUC) is working to site recycled water facilities in the city, develop groundwater supplies on the west side and make deep gains in conservation — no small feat in the most water-efficient city in California. By agreement with its wholesale customers, who use two-thirds of the water from the Hetch Hetchy system, the SFPUC must develop 10 million gallons a day of these additional supplies in San Francisco by 2018. This represents about 13 percent of the city’s current daily water use.

Not all of these alternative water supplies are created equal. Regulations — and common sense — currently prohibit us from drinking recycled water (i.e. treated sewage water), graywater (used kitchen, laundry or bath water) or seepage water (water that seeps into basements and needs to be pumped out), none of which are treated to drinking water standards. But these water sources are perfectly fine for uses such as flushing toilets, filling cooling towers or irrigating parks and can be used to offset our potable water demand. This way, we can save the very best Hetch Hetchy water for drinking.

To support this idea of matching supplies to appropriate uses — which is more efficient, sustainable and drought-resilient than using the same source for every use — the SFPUC recently evaluated the feasibility of “onsite” supplies to meet nonpotable demands. These are water supplies such as rainwater, graywater, blackwater (sewage) and seepage water that are generated, partially treated and reused on the same property. The SFPUC studied how much Hetch Hetchy water could be saved by aggressively encouraging the use of onsite supplies to meet nonpotable demands for residential, commercial and municipal open space uses. The study looked at the theoretical maximum available supply from sources such as rainwater or graywater and then looked at maximum feasible onsite demands for such sources. It concluded that in 2035, with 100 percent participation in these programs, San Francisco could save 3.4 million gallons a day.

Let’s put 3.4 million gallons a day in perspective. This savings is significant for a conservation program. It’s more than we will get from any one recycled water facility. It would add a significant extra and drought-resilient supply of local water, over and above the 10-million-gallon-a-day alternative supply portfolio San Francisco is developing from recycled water, groundwater and conservation. It would be a huge boon to the Tuolumne River and its ecosystems if we could put that extra water back into the river. We should pursue this new supply with gusto, first by making it easier to do onsite nonpotable reuse (which SPUR has strongly supported), then by creating greater incentives to do so.

But it will never replace the 74 million gallons a day that Hetch Hetchy delivers to San Francisco. We can’t reduce reuse, and recycle our way out of needing our region’s most important water system.

Read more about why we need Hetch Hetchy more than ever >>