How much it costs to build a desalination plant depends on which page of one state report you read

How much it costs to build a desalination plant, in one 2022 state plan

Desalination is the process of removing salt from ocean water or salty groundwater to make it safe to drink. How much it costs to build a desalination plant depends on which page of a government report a reader opens, because the same report can state 2 different costs for the exact same project. The 2022 Texas State Water Plan lists the cost to build each of 7 seawater desalination plants the state recommends, ranging from 40,290,000 dollars for a small plant proposed by the Laguna Madre Water District to 802,807,000 dollars for the Harbor Island plant proposed by the Port of Corpus Christi Authority, the Texas Water Development Board states in its own 2024 report.

One Texas Water Development Board report states 2 costs for 1 plant

One project on that list, the Corpus Christi Inner Harbor seawater desalination plant, sized to produce 20 million gallons a day, appears twice in the same 2024 Texas Water Development Board report, at 2 different prices. The 2022 state plan section of the report prices it at 236,693,000 dollars. A separate section of the identical report states that the Texas Water Development Board itself loaned the City of Corpus Christi 535,000,000 dollars for that same plant by August 2024, about 2.26 times the earlier figure, a calculation made for this article. Reading both sections of the 1 report directly, rather than a summary built from either figure alone, is what turns up the gap, since the authors of the report never point 1 section at the other. The loan is a loan, not a confirmed final construction cost, and no source states that the plant is finished or names a closed out total.

Why the price keeps climbing

Cost rises with the water going into the plant, not just the size of the plant, the Texas Water Development Board states. A reverse osmosis system, the technology used to remove salt, usually turns only half the seawater it takes in into fresh water, called the recovery rate, and a saltier intake demands more energy and higher cost to reach that rate. The United States Geological Survey states that desalinated water from the real Claude Bud Lewis Carlsbad Desalination Plant in California costs about twice as much as other water sources, because breaking the chemical bond that holds salt in water takes a lot of energy every day the plant runs. A peer reviewed engineering study modeled 2 versions of the same sized plant, each fed by a different sea, and found the saltier water raised the modeled cost to build from 50,595,704 dollars to 90,395,642 dollars, because the membranes that do the filtering, 61.72% of the modeled cost to build, have to work harder against saltier water. A California research nonprofit warned in 2012 that rising energy prices alone could push desalination costs higher still.

One agency answer, a fixed price before construction starts

South Coast Water District in California is building the Doheny Ocean Desalination Project, a 5 million gallon a day plant, at a total estimated cost of 175,000,000 dollars, more than 40,000,000 dollars of which the district has already covered through state and federal grants.

We lock in a guaranteed maximum cost for both capital and operations before we even commit to begin construction.

Rick Shintaku, General Manager of South Coast Water District. Source 5.

That contract structure is the opposite of what happened on the Corpus Christi Inner Harbor project, where the same government report shows the price moving after the first estimate was already public.