San Diego, a region once defined by its precarious water supply and strict conservation measures, is now positioned to sell millions of gallons of surplus water to its parched neighbours, Arizona and Nevada. The two desert states are negotiating a deal with the San Diego County Water Authority to purchase water produced by the largest ocean desalination plant in North America, a move that underscores a dramatic shift in Southern California’s water fortunes.
The potential agreement would provide a critical new water source for Arizona and Nevada, which are grappling with severe shortages from the historically low levels of the Colorado River. For decades, San Diego was almost entirely dependent on imported water, much of it from that same declining river. Now, thanks to strategic investments in a diverse and drought-proof water portfolio, the county has a surplus so reliable that it can be sold to other states in need.
At the centre of this remarkable turnaround is the Claude “Bud” Lewis Carlsbad Desalination Plant. The state-of-the-art facility, which began operations in 2015, uses reverse osmosis technology to produce tens of millions of gallons of high-quality drinking water from the Pacific Ocean every day. This desalinated water has become a cornerstone of the region’s supply, providing a locally controlled, drought-resilient source that is independent of snowpack and rainfall.
A remarkable reversal
Not long ago, San Diego was a poster child for urban drought vulnerability. The county imported about 95 per cent of its water in 1991, leaving it dangerously exposed to droughts, earthquakes, and environmental regulations that could restrict deliveries from Northern California and the Colorado River. This vulnerability prompted the San Diego County Water Authority to launch an ambitious, multi-decade strategy to diversify its water sources and reduce its reliance on imports.
This strategy involved a combination of approaches, including promoting aggressive conservation programs, securing new long-term transfer agreements for Colorado River water, and investing heavily in local supplies like groundwater and water recycling. The Carlsbad desalination plant, a project that was debated for years, represented the boldest and most expensive part of this diversification effort. Its success has fundamentally reshaped the region's water future.
The county now boasts one of the most diversified water supply portfolios in the country. The diversification strategy has proven so effective that even during statewide droughts, San Diego has maintained a stable supply. This resilience has not only secured water for its own 3.3 million residents but has also created an unexpected economic opportunity: becoming a water provider for other states.
A new model for the West
The proposed deal with Arizona and Nevada represents a new frontier in how water is managed in the arid American West. Instead of states fighting over dwindling shares of a shrinking river, one municipality is leveraging its own water security to provide a lifeline to others. While the details of the agreement are still under negotiation, it would involve the inland states paying San Diego for a portion of its desalinated water, which they would then receive in the form of an equivalent amount of Colorado River water that San Diego would forbear.
This arrangement allows the physical water to stay in the river system for use by entities in Arizona and Nevada, avoiding the impossible logistics of building a pipeline from San Diego. The deal provides a market-based solution to a regional environmental crisis, rewarding San Diego for its foresight and investment while providing much-needed relief to states facing the prospect of devastating water cuts.
The success of San Diego's strategy offers a potential blueprint for other coastal communities grappling with water insecurity. While desalination has its own environmental and economic challenges, including high energy consumption, San Diego has demonstrated that it can be a vital component of a resilient water supply when integrated into a broader portfolio of conservation and recycled water programs.
From wastewater to craft beer
San Diego's leadership in water innovation extends beyond desalination. The region is also a pioneer in water purification for reuse, a process that turns wastewater into potable drinking water. This technology, once derisively nicknamed "toilet-to-tap," has gained widespread acceptance as a safe and reliable water source.
To showcase the purity of the recycled water and build public trust, local breweries have famously used it to create craft beers, including IPAs and pilsners. This creative public relations effort highlights the immense scientific progress in water treatment and the region's innovative culture. The water is treated using a multi-stage process of micro-filtration, reverse osmosis, and advanced oxidation with ultraviolet light and hydrogen peroxide, resulting in water that is near-distilled in its purity.
This commitment to recycling complements the desalination efforts. It treats water as a reusable resource, reducing the amount of wastewater discharged into the ocean and creating another locally controlled supply. Like the surplus program at UC San Diego, which turns old equipment into revenue, the water authority's programs transform a liability, wastewater, into a valuable community asset.
As the deal with Arizona and Nevada moves forward, San Diego is cementing its new identity not as a victim of drought, but as a leader in water sustainability and a broker of water security for the broader region.
