Desalination will not solve California’s water woes

In the wake of the recent drought, desalination of ocean water continues to be a central topic in California water debates.

Some coastal communities were particularly hard hit by the drought, including a large swath of the central coast that is among the last regions in the state still suffering from drought conditions. Desalination seems to hold the potential for limitless, drought-proof supplies, but the reality is far more complex.

Desalination comes with the obvious downsides of very high capital costs and energy consumption, not to mention the high cost of operation and maintenance.

The potential impacts on ocean ecosystems have generated controversy and delays. In addition, communities are only start- ing to tap alternative sources, such as recycled wastewater and storm water, that have the potential to be less costly and more sustainable in the long-term. The decision whether to build a coastal desalination plant should be based on a consideration of all of these factors for each community.

Such decisions should not, however, be based on the hope that ocean desalination will fundamentally alter the state’s overall water budget and supply portfolio. More specifically, we cannot rely on ocean desalination to meaningfully reduce the stress on freshwater ecosystems, particularly the Bay Delta and its tributaries, the heart of California’s water supply.

Part of this is just due to the numbers. We withdraw approximately 42 million acre-feet per year from rivers, streams, and aquifers in California. We use up a net total of 33 million acre-feet of that. According to the 2013 update to the state’s water plan, even if every proposed ocean desalination facility were built (an unlikely scenario), they would produce a combined total of approximately 382 thousand acre-feet a year, less than 1 percent of the state’s existing water budget. Looking at just the Bay-Delta, humans use up or export approximately 6 million acre-feet per year. Again, even if all of the current ocean desalination proposals were built and run at full capacity, they collectively would not put a meaningful dent in our use of the Bay-Delta.

Furthermore, and just as importantly, there is no guarantee that every acre-foot of desalinated water would reduce demand on the Bay-Delta by an acre-foot. Currently there exists no systematic or legal mechanism to ensure that the water purveyors that opt into desalination facilities will directly reduce their reliance on the Delta.

To our knowledge, there is just one proposed desalination facility that will in fact reduce strain on a local freshwater ecosystem. The proposed California American Water plant near Monterey will directly reduce surface water withdrawals from the Carmel River. Those reduced withdrawals, however, were mandated by the state more than 20 years ago. Such mandates with direct links to meaningful improvements in stream flow should certainly be a factor in deciding whether to build a desalination plant. We are not aware, however, of any other proposed plant that can yet claim such a link.

While often Californians are persuaded to consider desalina- tion as a way to future water supply security using Israel and Western Australia as examples, one should remember that California is a highly populated state of about 40 million compared to 8 million in Israel and 2.6 million in Western Australia.

Seawater desalination, while can be a very small part of water supply portfolio of some of California’s coastal regions, will not be a significant part of the pie. The math is just not there.