Whenever California is pummeled by drought — as is still very much the case despite recent rain — a lot of people find themselves asking, “What if we got water from the ocean?”

In San Diego County, it’s already happening at a $1 billion facility by the beach.

Recently, as I reported on San Diego’s decadeslong quest for water stability, I visited the Carlsbad Desalination Plant, the largest such facility in the country, to see how it works.

The plant, which opened in 2015 after a long, fraught development, essentially creates 50 million gallons of fresh drinking water every day. Seawater flows through a massive intake pipe directly from the Pacific Ocean, where it first gets pumped into tanks that work sort of like Brita filters to take out bigger stuff — like algae — that shouldn’t be in drinking water.

Then the water makes its way through a labyrinth of pipes where more impurities are removed until basically just salt is left. This makes sure the water is ready for the signature, high-tech reverse osmosis desalination process, which takes place in thousands of tubes stacked high in a cavernous building. The loud hum of the machinery echoes through the space.

In each of those tubes, there are rolled up membranes that act like “microscopic strainers,” as officials describe them. The water is pushed through at a high pressure, and the membranes catch the salt and other dissolved minerals until all that’s left is pure H2O.


Finally, the water gets treated to make it more like normal drinking water, before it’s piped miles to be mixed in with the rest of the county’s water, and delivered to taps across San Diego. The salty brine that’s left over gets mixed in with seawater and pumped back into the ocean.

A relatively small proportion of the county’s water comes from the ocean — about 8%. Critics say that it’s some of the most expensive water that exists, and that operating the plant can harm the neighboring ocean ecosystem.

Officials with the San Diego County Water Authority and the private company that runs the plant, Poseidon Water, say that adding desalination has cost each household an average of $5 per month, and that they are constantly working to make the plant more environmentally friendly and energy efficient.

Above all, they say, the ocean is a rare drought-proof water source worth the investment for some level of certainty.

Other communities up the coast have taken notice amid the drought. Some are exploring seawater desalination plants of their own, while others are considering removing salt from brackish water in rivers. Another Poseidon Water plant is in the works for Huntington Beach.