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Frequently Asked Questions

About Hetch Hetchy Reservoir and the Regional Water & Power System

A View of Hetch Hetchy from Waapama Falls 

Can the water be stored elsewhere?
Due to the nature of the surrounding watershed, elevation and snowmelt source, the water collected in Hetch Hetchy Reservoir does not require filtration.

Shifting any of this water into other system reservoirs reduces water quality and would
require filtration for all system water. Shifting this storage would also negatively impact the system’s current ability to move water across the state by gravity, and eliminates 835 million kilowatt hours of clean, hydroelectric power.

Can the water be stored in existing local reservoirs?
Regional Water System reservoirs are intended to capture and store water from adjacent watersheds for delivery to water customers. Our Regional Water System local reservoirs (Calaveras, San Antonio, Crystal Springs, Pilarcitos, and San Andreas) do not have sufficient capacity to store Hetch Hetchy Watershed water and also capture adjacent local watershed runoff. 

Waterfall - Hetch HetchyWhy not simply enlarge the existing system’s local reservoirs?
Adding capacity to existing local reservoirs comes with a high environmental cost. Enlarging reservoirs floods additional acres of land and scenic rivers, thereby negatively impacting existing ecosystems. The Regional Water System’s existing local reservoirs are either in pristine or highly populated areas, or are adjacent to major faults, making the construction of additional storage extremely challenging and complex.

Why not store the water in Don Pedro Reservoir?
Don Pedro Reservoir is owned by the Modesto and Turlock Irrigation Districts, and stores their water for irrigation, flood control, and power generation. Although the Regional System banks water with the Districts, our agency has no legal water storage rights in Don Pedro, nor the rights to implement infrastructure changes at the Districts’ facility.

Why not simply build additional storage in Cherry Lake and Lake Eleanor?
Water stored in Cherry Lake and Lake Eleanor is used to satisfy senior water rights of the Modesto and Turlock Irrigation Districts, as well as for hydroelectric power generation and
fishery purposes. The watersheds surrounding these reservoirs do not empty into Hetch Hetchy Reservoir, and additionally, due to their smaller size, collect significantly less water.
Water diverted from these reservoirs for Bay Area use would require filtration. Additionally, Lake Eleanor lies wholly within Yosemite National Park, thus any expansion of water storage would require Congressional approval.

Can we eliminate the need for Hetch Hetchy Reservoir by utilizing local water supplies and conservation?
Regardless of storage capacity, local precipitation in the San Francisco Bay Area is not sufficient to consistently supply the diverse water needs of 2.6 million commercial and residential customers. It is much less plentiful than the rain and snow of the Tuolumne Watershed. San Francisco’s residential water use is already one of the lowest of any major urban area in California. In addition, local water supply and conservation projects are already in progress, and are projected to reduce Regional Water System demand by 20 million gallons per day by 2030. These projects include passive and aggressive conservation, increased production and use of recycled water for non-potable uses, and use of groundwater for drinking.

Streetlight - atmosphereIs Hetch Hetchy hydropower renewable and clean?
Yes. Hetch Hetchy hydroelectric energy is clean, efficient and dependable. Hetch Hetchy hydroelectric energy does not emit any greenhouse gases, produce harmful radioactive byproducts, or leave behind any waste or byproduct of any kind. The Hetch Hetchy Power System supplies 100% of San Francisco’s municipal energy usage and lessens its reliance on costly energy purchases for municipal use, such as City streetlights, SF General Hospital, SF Airport, SFUSD public schools, and the MUNI transportation system.

Can the same amount of power be generated on the river using flow-through dams?
‘Flow-through’ or ‘run-of-the-river’ power plants are dependent on the flow of water during wet and dry seasons. As such, these types of power generation facilities cannot consistently generate the amount of power that the current system generates.

The Tuolumne River above Hetch Hetchy Reservoir and downstream to Don Pedro Reservoir is a federally-designated Wild and Scenic River. Many parts of the watershed are federally-protected
Wilderness. Construction of any new power generation facility on the Tuolumne River would require removing pristine areas from federal protection, building permanent transmission lines
and access roads, and destroying protected habitats.

Does retaining Hetch Hetchy Reservoir prolong ongoing destruction of one of the most diverse ecosystems in the world?
The Hetch Hetchy Regional Water System, in partnership with the National Park and U.S. Forest Services, protects over 652 square miles of High Sierra wilderness, which surround the Hetch Hetchy, Lake Eleanor, and Cherry Creek watersheds. These highly protected lands support unique, diverse wilderness ecosystems. The Regional Water System contributes more than $5 million annually to the National Park Service to protect these lands and maintain trails and roads.

The system also provides ongoing wilderness and watershed education to park visitors. Removal of Hetch Hetchy Reservoir would greatly change current upstream and downstream ecosystems, as well as negatively impact other diverse ecosystems and open space wherever
replacement reservoir storage was built.

Wouldn't tearing down O’Shaughnessy Dam and rebuilding San Francisco’s water system elsewhere be good for the environment?
The carbon footprint of the existing system is one of the smallest of any water system in the United States. Removing the dam would require system-wide filtration and almost certainly pumping of water, both energy-intensive processes that would increase our greenhouse-gas emissions. Even the energy required simply to tear down the dam – including removal of some 600,000 cubic yards of concrete – would substantially increase greenhouse-gas emissions.

Is it a good idea to remove O’Shaughnessy Dam?
Removing O’Shaughnessy Dam would require the complete re-engineering of a clean, efficient water and power delivery system that serves over 2.6 million people on a daily basis. The State of California estimated re-engineering costs to be anywhere from $3 billion to $10 billion. Re-engineering the entire system would have significant implementation and operational costs, negative impacts on water supply reliability and water quality, effects on legal rights to property and water, and a cascading impact on statewide water allocations and agreements.

O'Shaughnessy DamWouldn’t it only cost $1 billion to remove the Hetch Hetchy Dam and restore the Valley?
No. A comprehensive, independent State of California – Department of Water Resources study in 2006 estimated the costs of re-engineering the system and restoration of the Hetch Hetchy Valley to be anywhere from $3 billion to $10 billion.

Can costs be minimized by simply ‘puncturing’ the dam?
The cost of puncturing O’Shaughnessy Dam is a minimal component of any plan to cease water storage in Hetch Hetchy Reservoir. The costs truly represent three colossal projects: a re-engineering of the existing water system (conveyance, storage and treatment); environmental restoration; and the replacement of lost hydropower and power infrastructure.

Any changes to this regional system would require addressing not only the replacement of water storage from Hetch Hetchy Reservoir, but also

  • Reduced water quality and resulting increased treatment requirements
  • Annual loss of 835 million kilowatt hours of clean, dependable hydroelectric generating capacity, and resulting in increased regional energy purchases
  • Required infrastructure changes to rebuild the water and power delivery system
  • Legal rights to water, water delivery agreements, infrastructure and property
  • All financial and environmental costs associated with making these required changes
Last updated: 6/4/2012 2:43:29 PM