San Luis Obispo County supervisors on 1 September 2026 received a presentation on a $1.2 million feasibility study that lays out where the county could build a seawater desalination plant, how much it would cost and which communities the water could serve, according to the San Luis Obispo Tribune. The county will not pursue a project this year, but the study is meant to guide a future effort if regional partners step forward.
Key takeaways
- San Luis Obispo County has completed a $1.2 million feasibility study for a seawater desalination plant, presented to the Board of Supervisors on 1 September 2026 (San Luis Obispo Tribune).
- Five siting options are on the table, with construction estimates ranging from about $179 million at Cambria to $545 million at Morro Bay (San Luis Obispo Tribune).
- Annual output across the options spans roughly 330 to 7,135 acre-feet, with the Morro Bay and South SLO sites offering the largest deliveries to the most communities (San Luis Obispo Tribune).
- Any future build faces a multi-decade process of further studies, permitting, funding and construction, and no partner agency has yet volunteered (San Luis Obispo Tribune; KSBY News).
What happened
The county's existing portfolio of groundwater, reservoirs, recycled water and state water all depends on rainfall, and San Luis Obispo County Public Works Deputy Director Courtney Howard told the board that desalination produces drinking water regardless of the weather, the San Luis Obispo Tribune reported. County engineer Angela Ford, in the same presentation, described a reverse-osmosis plant that would draw seawater through a submerged pipe and discharge brine through a marine outfall, ideally one tied to an existing wastewater treatment plant so the brine can be diluted in effluent before release, the San Luis Obispo Tribune reported.
Five candidate sites were laid out with capital and yield figures, as reported by the San Luis Obispo Tribune:
| Site | Construction cost (reported) | Annual yield (acre-feet) | Potential users | Outfall |
|---|---|---|---|---|
| Cambria | about $179 million | 330 to 580 | Cambria, San Simeon | New outfall required |
| Cayucos (Estero Marine Terminal) | about $261 million | 930 to 1,055 | Cambria, San Simeon, Los Osos, possibly other inland communities | Existing Estero Marine Terminal outfall |
| Morro Bay | about $545 million | 5,855 to 7,135 | Cambria, San Simeon, Los Osos, Templeton, Lopez Lake users, San Luis Obispo, Cal Poly | City wastewater treatment plant outfall |
| Near South SLO Wastewater Treatment Plant | about $483 million | 5,070 to 6,825 | Nipomo, Arroyo Grande, Grover Beach, Oceano, Avila Beach, San Luis Obispo, Cal Poly, Los Osos, groundwater sustainability agencies | South SLO plant outfall |
| Former Nipomo Mesa Refinery | about $254 million | 1,805 to 1,905 | Nipomo, Arroyo Grande, Grover Beach, Avila Beach, Pismo Beach, Oceano, possibly Santa Barbara County users | Existing refinery outfall |
Morro Bay is not currently on the user list because the city is exploring a recycled water project first, and no agency has yet stepped up to take any of the sites forward, the San Luis Obispo Tribune reported. A community survey was opened earlier in 2026 as part of the county's five-phase public engagement process, with the KSBY News reporting a 20-year-plus timeline before any approved facility would be functional.
Board members were split. Supervisor Bruce Gibson told the board the cost of desalinated water is "eye-watering" and pushed for cheaper resilience options first, while Supervisor Heather Moreno argued the county cannot wait: "We can't wait until we need it," she said, according to the San Luis Obispo Tribune. Supervisor Jimmy Paulding said the county "probably need desal in the future" and should keep working toward that end, the same outlet reported.
Specification read
The headline capacity, taking the Morro Bay upper bound of 7,135 acre-feet per year, converts to roughly 7,500 m³/day (1 acre-foot ≈ 1,234 m³, 365-day year). The Cambria lower bound of 330 acre-feet is about 1,115 m³/day, a small municipal supply class. Reported capital intensity at Morro Bay works out to roughly $70 to $80 per m³ of daily design capacity at the high-yield end (general industry range, not from the sources), against a typical seawater RO benchmark in the tens of dollars per m³/day (general industry range, not from the sources); the gap reflects the high fixed cost of outfall, intake and marine works for a coastal California site of this size.
For a project of this class, the treatment train is seawater intake screening and fine filtration, cartridge filtration, two-pass reverse osmosis with energy recovery, post-treatment re-mineralisation and corrosion control, then disinfection before distribution, with the brine line tying into a wastewater treatment plant outfall for dilution. The SLO study bears on the front-end (intake, pretreatment, high-pressure RO) and the back-end (brine discharge, outfall integration) of that train, both of which are where most of the project cost and most of the permitting risk sit. For a plant operator scoping a similar coastal potable reuse or industrial reuse line in the 1,000 to 10,000 m³/day band, the practical read is that RO membrane skid selection, energy recovery device sizing and outfall consent will drive both the capex number and the 20-year schedule cited by local officials, and the relevant product families to evaluate are Water Purification and Mbr Membrane Systems. The choice between membrane desalination and ion-exchange polishing is downstream of the RO train and is covered in side-by-side cost comparisons for process wastewater reuse, for example RO vs Ion Exchange for F&B Process Wastewater: 2026 OPEX Comparison and RO vs Ion Exchange for API and Formulation Wastewater: 2026 OPEX Verdict for Cooling Blowdown Reuse.
FAQ
What did San Luis Obispo County actually decide on 1 September 2026?
Supervisors received the $1.2 million feasibility study and the five siting options. No project is being built this year; the county is keeping the study on file for a future push when a partner agency volunteers, according to the San Luis Obispo Tribune.
How much would a desalination plant cost and how long would it take?
Reported construction estimates run from about $179 million (Cambria) to about $545 million (Morro Bay), with the KSBY News citing a timeline of more than 20 years from greenlight to operation. For reference, large seawater RO plants elsewhere typically deliver water at $1 to $3 per m³ all-in (general industry range, not from the sources), so the operating cost will be a bigger fight than the headline capital figure.
Which site is the strongest candidate for procurement teams to watch?
On reported numbers the Morro Bay and South SLO sites carry the largest yields (up to 7,135 and 6,825 acre-feet per year) and the broadest user base, but they are also the costliest ($545 million and $483 million) and Morro Bay is not currently on the user list, per the San Luis Obispo Tribune. Procurement teams should treat all five as options, not as a shortlist.
What should a buyer scoping a similar project be asking suppliers right now?
Pin down intake and pretreatment design flow in m³/day, RO membrane type and replacement interval, energy recovery device specification, and outfall consent conditions including brine dilution ratios, because these drive both capex and the multi-decade permit path described by the KSBY News. Ask vendors for guaranteed specific energy consumption in kWh per m³ of permeate and for a reference plant in the same flow band (general industry range, not from the sources).
