San Diego is the driest major city in the continental United States, receiving about 10 inches of rainfall per year. With essentially no local water supply, it imports 80–90% of its water from two distant sources: the Colorado River (via the Metropolitan Water District of Southern California) and the State Water Project (from Northern California). About 10% comes from a small desalination plant in Carlsbad — the largest ocean desalination facility in the Western Hemisphere — and from local reservoirs.
This imported water system produces water that is safe by federal standards, but that arrives heavily laden with the minerals and organic matter from its long journey. The result is some of the hardest water among major US cities and consistently elevated disinfection byproduct levels.
A new wrinkle as of 2026: Sweetwater Authority, serving 200,000 residents in South San Diego County, has PFAS in its Sweetwater Reservoir — and the levels have been fluctuating.
Where San Diego's Water Comes From
Metropolitan Water District / Colorado River: The Colorado River water that reaches San Diego originates as Rocky Mountain snowpack and accumulates minerals — particularly calcium and magnesium — throughout its passage through the arid Southwest geology. By the time it reaches Southern California, it's very hard water with significant dissolved mineral content.
State Water Project: Water pumped from the Sacramento-San Joaquin Delta in Northern California, then transported 700+ miles south through the California Aqueduct. Softer than Colorado River water but still carries organic content from the Delta environment.
Carlsbad Desalination Plant (Claude J. Bud Lewis facility): Produces approximately 50–60 million gallons per day of highly purified seawater. The desalination process uses reverse osmosis — meaning the desalinated water has extremely low TDS and virtually no contaminants. However, it's blended with harder imported water before distribution, moderating (but not eliminating) the hardness problem.
Local reservoirs: Several local reservoirs catch what limited rainfall there is. These have lower mineral content but contribute a small fraction of overall supply.
The San Diego County Water Authority provides water wholesale to more than 20 local agencies including San Diego Public Utilities, Sweetwater Authority, Otay Water District, and others — meaning water quality varies somewhat by which agency serves your neighborhood.
What's in San Diego Tap Water in 2026
Hardness: 12–16 GPG — Very Hard
San Diego consistently ranks among the top five hardest water cities in the US. The Colorado River water arrives at roughly 15–16 GPG after blending and treatment. Some areas receiving more State Water Project supply have slightly lower hardness.
The practical effects are the same as elsewhere with very hard water: scale deposits throughout the plumbing and appliances, spots on dishes and glassware, reduced appliance lifespans. In a city where water costs are among the highest in the country (a consequence of the long-distance import system), hard water-damaged appliances are a real financial concern.
PFAS: Active Situation at Sweetwater Authority
This is the current story. As of January 2026 testing, Sweetwater Authority found PFAS at the Sweetwater Reservoir — five PFAS compounds detected out of the 29 they're required to test for. The agency first disclosed this issue in 2024, and levels have been fluctuating, with the January 8, 2026 test showing the lowest levels since the prior year.
The PFAS are below the new EPA MCLs (4 ppt for PFOA/PFOS), and Sweetwater officials say the water is safe to drink. But the agency is taking this seriously — community workshops have been held, and the agency is exploring treatment options. A key challenge: if PFAS levels increase further, the cost of treatment (activated carbon or RO at the plant level) may require rate increases.
The source: PFAS don't occur naturally — they come from upstream human activity. The SDCWA notes its imported Metropolitan Water District supplies have occasionally found PFAS at trace levels in some source waters. The San Diego Water Board has regulatory oversight of potential local DoD and industrial sources (Camp Pendleton, Coronado, and Warner Springs are all noted PFAS sources from AFFF use at military installations).
For the broader San Diego County Water Authority supply (which isn't the same as Sweetwater's local reservoir), the desalinated Carlsbad water is PFAS-free (RO removes PFAS), and PFAS testing of imported supplies shows generally very low or below-detection levels at the treatment plants.
Action for Sweetwater customers: If you're served by Sweetwater Authority (Chula Vista, National City, Bonita, Spring Valley, and surrounding areas), the current data shows levels below EPA MCLs. For peace of mind, RO at the kitchen tap removes PFAS effectively.
Disinfection Byproducts: Elevated
San Diego's TTHM and HAA levels are among the higher in California. Reported TTHM levels of up to 75.6 ppb (near the 80 ppb federal MCL) and HAA5 up to 19 ppb have been recorded. The EWG database shows HAA9 levels 302x above their health guideline.
The mechanism is the same as Atlanta and Houston: organic material in imported surface water reacts with chlorine disinfection to produce halogenated byproducts. The Colorado River water is particularly organic-laden relative to softer, cleaner mountain sources.
Chromium-6: Above EWG Guideline
San Diego water has tested for chromium-6 at levels up to 0.36 ppb — about 18x the EWG health guideline of 0.02 ppb, though below California's new 10 ppb MCL (effective October 2024). Geological sources from the Colorado River and Southern California geology contribute.
Arsenic: Below Federal Limit, Above EWG Guideline
Arsenic levels around 2 ppb have been reported — below the federal 10 ppb MCL but above EWG's 0.004 ppb health guideline. Geological origin from the Colorado River watershed.
Lead: Low Concern in New Infrastructure, Risk in Older Homes
San Diego Public Utilities tests show no detectable lead in treated water leaving the plants. Lead enters via building plumbing, particularly pre-1986 homes with lead solder. San Diego's newer neighborhoods (post-1990s construction, common in North County) have very low lead risk. Older neighborhoods (North Park, South Park, Golden Hill, Hillcrest, Barrio Logan) may have pre-1986 plumbing.
The San Diego Unified School District has installed filtered hydration stations and set a 5 ppb internal lead limit — stricter than the federal 15 ppb action level — reflecting awareness of the risk in older school buildings.
→ Check your specific San Diego ZIP's water quality at PureCity
The Right Filter Strategy for San Diego
San Diego's combined problem is: hard water damaging appliances + elevated DBPs + PFAS concern at Sweetwater + trace arsenic and chromium-6. The optimal solution depends on your situation.
For drinking and cooking water — the universal recommendation:
An under-sink RO system addresses all of San Diego's priority concerns simultaneously: hard water minerals, DBPs, PFAS, chromium-6, arsenic, and lead. Given San Diego's water profile, this is one of the clearest RO use cases in the US.
- APEC ROES-50 (~$215) — NSF 58 certified; removes all San Diego priority contaminants; standard recommendation
- iSpring RCC7AK (~$219) — adds remineralization; since RO strips San Diego's hard water completely, remineralization improves taste significantly
- Bluevua RO100ROPOT-LITE Countertop RO (~$299) — countertop, no installation; ideal for renters in San Diego's large apartment market
For whole-house hard water protection:
A salt-based ion exchange softener is the standard solution for San Diego's 12–16 GPG hardness. California restricts salt softeners in some areas (Santa Clara County, parts of LA) due to chloride in wastewater — check your local rules, but San Diego County does not currently restrict them.
A salt-free TAC conditioner (template-assisted crystallization) is an alternative that reduces scale without adding sodium and is always permissible — better suited for renters and condos.
Best pitcher if installation isn't feasible:
- Clearly Filtered Pitcher (~$90) — certified for PFAS, chromium-6, lead, and DBPs; the best non-RO option for San Diego's contaminant profile
Sweetwater Authority Resources
- Community water quality updates: sweetwater.org
- Address lookup for PFAS testing results: available at Sweetwater's website
- Free PFAS information workshops: being held through 2026
The Bottom Line for San Diego Residents
San Diego's water is federally compliant and safe against acute illness. The practical concerns are: scale damage from extreme hardness, elevated DBPs from organic-rich imported source water, and the emerging PFAS situation at Sweetwater Authority specifically. For Sweetwater customers in South County, the current levels are below federal action thresholds but warrant monitoring.
For all San Diego residents, an RO system at the kitchen tap is a strong match for the local water profile — addressing hard water minerals, DBPs, PFAS, arsenic, and chromium-6 in one system.
Related Articles
- Hard Water: What It Actually Does to Your Home, Your Health, and Your Appliances
- PFAS in Drinking Water: What It Is, Where It's Found, and How to Filter It
- Chromium-6 in Drinking Water: The 'Erin Brockovich Chemical' With No Federal Limit
- Best Under-Sink Reverse Osmosis Systems
Sources: San Diego County Water Authority: Water Quality · Sweetwater Authority PFAS / Forever Chemicals in Sweetwater Reservoir, inewsource, March 8, 2026 · San Diego Regional Water Quality Control Board: PFAS · Hydroviv: San Diego Water Issues · EWG Tap Water Database: San Diego · California State Water Board: Hexavalent Chromium MCL