Pure Water: San Diego Is Building a Second Water Supply Out of Its Own Tap
The city's Pure Water program will recycle wastewater to drinking-water standards at a scale few American cities have attempted. We read the program documents to see what it promises — and what it depends on.
San Diego's defining resource fact is dependence. The city imports the great majority of its water — its own planning documents have long put the figure at roughly 85 percent — through aqueducts from the Colorado River and Northern California. Pure Water San Diego, the city's multi-phase potable reuse program, is the long-planned answer: treat the city's wastewater to drinking-water standards and use it to supply a large share of the city's needs locally.
The mechanics are established technology, assembled at unusual scale. Wastewater already treated at the North City Water Reclamation Plant gets additional purification — membrane filtration, reverse osmosis, and ultraviolet disinfection with advanced oxidation — producing water that meets or exceeds drinking standards. Phase 1, under construction in the northern part of the city, routes that purified water to Miramar Reservoir, from which it flows to the Miramar Water Treatment Plant and into the distribution system.
The program's promise, as laid out in city documents, is substantial: at full build-out across its phases, Pure Water is designed to provide close to half of San Diego's water supply locally, drought-proofed against the Sierra snowpack and Colorado River negotiations that govern imported supplies. The city's existing demonstration facility has run the purification train for years and produced a long public record of water-quality testing — thousands of analyses the city has published to make its safety case.
The dependencies are equally plain in the documents. Pure Water is a multi-billion-dollar construction program financed substantially through water rates, on a schedule set by regulatory agreements with the state over ocean discharge from the Point Loma treatment plant. Delays in construction translate directly into continued reliance on the Point Loma outfall and continued purchases of imported water.
The annual drinking water quality report the Public Utilities Department publishes each year — the tap-water report card every customer can read — is the baseline against which the new supply will eventually be judged. The city's case, in the end, is not rhetorical. It is a set of test results, and residents can hold it to exactly that standard.