2026-06-26

Desalination in California, Part I:

The Scope of the Problem

A Water Policy Series — June 2026

Introduction

Twelve miles apart on the Orange County coast sit two desalination projects that tell opposite stories. In Huntington Beach, a fifty-million-gallon-a-day plant proposed by Poseidon Resources was unanimously killed by the California Coastal Commission in May 2022. In Dana Point, a smaller, five-million-gallon-a-day plant called Doheny cleared its final federal environmental review in March 2026 and is on track to open by 2029. Same coastline, same state regulators, same general technology — opposite outcomes. Understanding why requires understanding what desalination actually costs, what it actually produces, and what it is actually being asked to solve. This is the baseline the rest of this series builds on.

I. Two Plants, One Dividing Line

Huntington Beach proposed an open intake pipe drawing water directly from the ocean. Doheny uses subsurface slant wells — buried beneath the seafloor, filtering seawater through sediment before it ever reaches a pump.¹ That single design choice decided both projects’ fates. California’s Ocean Plan, amended in 2015 to add statewide Desalination Provisions, makes subsurface intake the default-required technology unless a developer can show it isn’t feasible.² Open intakes kill and injure marine life through two mechanisms: impingement, where fish are trapped against intake screens, and entrainment, where eggs, larvae, and plankton are drawn into the system and destroyed. The State Water Board has used the impact data from an adjacent open-intake power plant as a proxy to quantify exactly how much fish biomass an open-intake desal plant would cost a local population — and at Huntington Beach, that cost, combined with sea-level rise flooding risk at the proposed site, was enough to sink the project.³

The operating precedent — the Claude “Bud” Lewis Carlsbad plant, the nation’s largest, online since 2015 — never had to clear this particular bar; it uses open intake and instead pays for the resulting harm after the fact, funding roughly 150,000 square meters of wetland restoration in the adjacent Agua Hedionda Lagoon as ecological compensation.⁴ That distinction matters for how the rest of this series treats desalination’s environmental cost: it is not a fixed cost of the technology, but a cost that regulators have learned to push toward prevention (subsurface intake) rather than compensation (wetland offsets) — at the price of a far more demanding permitting process.

II. What It Costs

Desalination is, by a wide and consistent margin, the most expensive water supply option California has. Carlsbad’s water runs $3,400 to roughly $4,000 per acre-foot; Doheny is projected at about $2,058 per acre-foot in its first year, cheaper but still well above conventional supply.⁵ Compare that to the alternatives: stormwater capture costs as little as $0.48 per cubic meter for large projects; conservation and efficiency programs run $600–$1,800 per acre-foot; wastewater recycling for indirect potable reuse runs roughly $700–$1,200 per acre-foot net in San Diego’s own estimates; and managed aquifer recharge runs about $1,200 per acre-foot on a capital basis.⁶ Desalination is two to six times more expensive than every one of them. California’s own official Water Supply Strategy reflects this ranking explicitly, sequencing recycling and stormwater capture ahead of desalination and treating desal as a last-resort tool rather than a first choice.⁷

The ratepayer consequence is concrete and already visible. San Diego is now the fourth most expensive municipal water market in the country.⁸ The San Diego County Water Authority originally projected desalination would add about $5.14 a month to the average household bill when 2016 rates were set; costs have run well past that since, with an 8.3% wholesale rate increase in 2026 alone pushing the average combined water/sewer bill up $22 a month, and further increases of 14.5%, 11.5%, and 11% already scheduled through 2029 — a roughly 60% cumulative rise.⁹ Desalination is not the sole driver of that increase, but it is consistently the most expensive line item in the supply portfolio, and the contractual structure compounds the problem: the Water Authority is locked into a take-or-pay agreement with Carlsbad’s owner obligating it to purchase a fixed volume of water every year through 2045 regardless of actual need. A 2025 investigation found ratepayers had been billed $35 million for water the plant never even produced.¹⁰

Energy is a meaningful share of that cost. Modern reverse-osmosis plants run roughly 3,500 kilowatt-hours per acre-foot at the treatment stage; Poseidon’s own regulatory filing for Carlsbad cited nearly 4,900 kilowatt-hours per acre-foot once delivery is included.¹¹ At a representative $0.30 per kilowatt-hour, that electricity alone costs on the order of $1,050 per acre-foot — meaning energy price volatility flows almost directly into water price volatility in a way it does not for recycled or imported supply. Statewide, the aggregate load is small — a million acre-feet of desalinated water would draw roughly 3,500 gigawatt-hours, about one percent of California’s total annual electricity consumption — but locally, a single large plant is a substantial, continuous new load; Carlsbad alone is reported to use enough power for some 35 small towns.¹² Whether that local load is met by renewable generation or by the marginal, often gas-fired generation that fills in around intermittent renewables is not well documented for California’s existing plants — a genuine gap in the public record, not a settled fact in either direction.

III. What It Produces, Against What’s Needed

California manages roughly 40 million acre-feet of water a year, split roughly 40% agricultural, 50% environmental, and 10% urban use, with agriculture alone consuming about 34 million acre-feet across 9.6 million irrigated acres in an average year.¹³ The state projects climate change could cut total supply by 6 to 9 million acre-feet by 2040, and has set a matching target to close that gap through four levers: 4 million acre-feet of new wet-year storage, recycling targets rising to 1.8 million acre-feet a year by 2040, 500,000 acre-feet a year freed through conservation, and new supply from desalination and stormwater capture.¹⁴

Set against that target, desalination’s actual contribution is small. Carlsbad produces about 56,000 acre-feet a year; Doheny will produce roughly 5,600. A dozen Carlsbad-scale plants statewide — a genuinely enormous, decades-long buildout — would supply under 700,000 acre-feet a year, less than a tenth of the projected gap.¹⁵ Brackish (non-coastal) desalination is actually the larger and faster-growing category in volume terms, with the state targeting 28,000 acre-feet a year of new brackish capacity by 2030 and 84,000 by 2040 — modest numbers next to the recycling and storage targets they sit beside.¹⁵ Desalination, in other words, is not positioned by the state’s own numbers to be a primary lever for closing California’s supply gap. Its case rests on a different property entirely: unlike every other lever in that strategy, its output does not depend on rain.

IV. Climate Change Cuts Both Ways

That drought-independence is becoming more valuable and more contested at the same time. Sierra snowpack — currently providing up to a third of the state’s water by storing winter precipitation for release through the dry season — is projected to fall to roughly two-thirds of historical levels by 2050, and what does fall is increasingly melting earlier and faster, arriving before it’s needed rather than during the summer months when demand peaks.¹⁶ California already has the most variable year-to-year precipitation in the continental United States, and that variability is intensifying into what climate scientists call hydroclimate whiplash: longer droughts punctuated by fewer, more extreme wet events, as a warming atmosphere holds and releases roughly seven percent more water per degree Celsius of warming.¹⁷ Every other tool in the state’s portfolio — recycling, conservation, recharge, storage — depends to some degree on that increasingly unreliable precipitation signal. Desalination, drawing from the ocean, does not.

But the same warming climate that strengthens desalination’s rationale also threatens where it can physically operate. Sea-level rise drives saltwater intrusion into coastal aquifers independent of anything a desal plant does, and the basins most exposed — the Pajaro and Salinas Valleys, the Oxnard Plain, the urbanized coastal plains of Los Angeles and Orange Counties — are largely the same basins where desalination projects are sited or proposed.¹⁸ This is not a future hypothetical: sea-level rise flooding risk at the proposed site was one of the explicit reasons the Coastal Commission cited in killing Huntington Beach.¹⁹ The technology California is leaning on precisely because it doesn’t depend on rain is sited in places increasingly vulnerable to a different consequence of the same warming climate.

V. The Counter-Case: Managed Aquifer Recharge

Set desalination’s profile against its cheapest serious rival and the contrast sharpens rather than softens. Managed Aquifer Recharge — and specifically Flood-MAR, a named California Department of Water Resources program — redirects flood-stage winter runoff onto farmland, floodplains, and flood bypasses to infiltrate and replenish groundwater, largely using existing irrigation and flood-control infrastructure rather than new treatment plants.²⁰ On cost alone it beats desalination by roughly a factor of three: about $1,200 an acre-foot on a capital basis, against desalination’s $2,700–$4,000-plus.²¹

The more important contrast is structural, not just financial. Every desalination mitigation measure catalogued in this series — wetland restoration to offset fish loss, multiport diffusers to dilute brine, subsurface intake to avoid entrainment in the first place — exists to cancel out a harm the technology itself creates. Flood-MAR’s benefits run the other direction. Diverting artificially elevated peak flows back toward their natural seasonal range reduces streambank erosion and channel scouring as a direct effect, not a purchased offset. Recharging groundwater during wet periods sustains higher dry-season baseflow, which keeps streams cooler and preserves over-summering habitat for juvenile salmon and other native fish — California’s Department of Water Resources specifically cites Chinook salmon as a beneficiary.²² Desalination needs mitigation to avoid making things worse. Flood-MAR makes a downstream ecosystem measurably better as a byproduct of doing its job. And because groundwater already supplies 40 to 60 percent of California’s water depending on the year, MAR is replenishing the resource the state already depends on most, rather than building an entirely parallel one.²³

But MAR’s advantage is conditional in a way desalination’s is not, and the condition is precipitation. During California’s 2012–2016 drought, Central Valley groundwater storage lost an estimated 28 cubic kilometers — roughly 22.7 million acre-feet — and less than a third of that has ever been recovered.²⁴ The reason is structural, not a failure of effort: in any given wet year, the excess streamflow actually available to divert into recharge basins statewide is capped at roughly 1.2 million acre-feet, and even in the wet years immediately following the 2012–2016 drought, median aquifer recovery reached only about 19 percent of the overdraft.²⁵ MAR cannot manufacture water that isn’t falling. It is, by design, a wet-year tool — exactly the tool that does the least good in the exact years, the multi-year droughts, when reliable supply matters most. That is the one gap in California’s portfolio that only a precipitation-independent source can fill, and it is the only part of desalination’s case that survives the cost comparison in this article on its own terms.

Conclusion

Desalination in California is expensive, energy-intensive, ecologically costly in ways that require active mitigation rather than generating it, and structurally a small contributor to the volume the state actually needs. Its cheapest serious rival, managed aquifer recharge, beats it on cost and produces ecological benefits rather than harms requiring offset — but only in years wet enough to recharge from, which is precisely when California needs supply the least. Desalination’s whole case rests on covering the years MAR cannot reach. That is a real and narrow justification, not the broad one often made for it, and the gap between the two is becoming both more valuable and, because of where these plants have to sit, more precarious as the climate changes. The next article turns to who is actually deciding how much of each tool California builds, and on whose behalf.

Footnotes

Sources

Government & Regulatory

California State Water Resources Control Board — Ocean Plan Desalination Provisions, Carlsbad regulatory record — waterboards.ca.gov

California Department of Water Resources — Water Supply Strategy, Desalination Resource Management Strategy, statewide allocation reports — water.ca.gov

U.S. Geological Survey — coastal groundwater hazards, sea-level rise — usgs.gov

Research & Policy Analysis

Pacific Institute — The Cost of Alternative Water Supply and Efficiency Options in California — pacinst.org

Public Policy Institute of California — Water Use in California; Climate Change and California’s Water — ppic.org

UC Davis Environs — When Desal in California Gets the Green Light: A Comparison of Four Projects — environs.law.ucdavis.edu

California Policy Center — Rebuilding California’s Infrastructure (Desalination) — californiapolicycenter.org

Journalism

CalMatters — A salty dispute; How can California boost its water supply? — calmatters.org

LAist — Plan For Huntington Beach Desalination Plant Is Rejected — laist.com

Voice of San Diego — San Diegans Owe a Desal Company $35 million for Unmade Water — voiceofsandiego.org

San Diego Coastkeeper — Why Is Your Water Bill So High?; Potable Reuse vs. Desalination — sdcoastkeeper.org

Coyote Gulch — San Diego: America’s 4th most expensive municipal water — coyotegulch.blog

UCLA Newsroom — snowpack and hydroclimate whiplash reporting — newsroom.ucla.edu

NRDC — California’s Climate Whiplash — nrdc.org

Managed Aquifer Recharge / Flood-MAR

California Department of Water Resources — Flood-Managed Aquifer Recharge program; Going with the Flow: How Aquifer Recharge Reduces Flood Risk — water.ca.gov

California Flood-MAR Hub — floodmar.org

California WaterBlog — A Functional Flows approach to implementing Flood-MAR — californiawaterblog.com

Science for Conservation — Benefits and Economic Costs of Managed Aquifer Recharge in California — scienceforconservation.org

Alam et al. — Can Managed Aquifer Recharge Mitigate the Groundwater Overdraft in California’s Central Valley?; Post-Drought Groundwater Storage Recovery in California’s Central Valley — Water Resources Research, agupubs.onlinelibrary.wiley.com

Stanford Doerr School of Sustainability — Groundwater in California’s Central Valley may be unable to recover from past and future droughts — sustainability.stanford.edu