Is San Diego, CA Tap Water Safe to Drink?

Where Does San Diego Get Its Water?

San Diego's drinking water is supplied by eight separate water utilities serving different parts of the city and surrounding communities. The primary provider is the City of San Diego's water system, but residents may also receive water from Helix Water District, Sweetwater Authority, Otay Water District, Olivenhain Municipal Water District, Cal-Am Water Coronado, the City of Del Mar, or Santa Fe Irrigation District, depending on where they live.

Several major treatment plants process water before it reaches your tap. The Alvarado Water Treatment Plant and Miramar Water Treatment Plant are two of the largest facilities in the city system. Other significant plants include the Levy Filtration Plant, Olivenhain Water Treatment Plant, Otay Water Treatment Plant, Perdue Water Treatment Plant, R.E. Badger Filtration Plant, and the National City Wells Plant.

Some utilities in the region receive water through interconnections with the San Diego County Water Authority rather than treating it entirely on their own. This blending of locally treated and imported water is common in Southern California, where regional supply reliability is a long-standing infrastructure priority.

How Is San Diego Tap Water Treated?

San Diego's water systems use a multi-step treatment process. Raw water typically goes through coagulation to clump particles together, followed by dissolved air flotation or conventional settling, and then filtration through membranes or granular media. Some systems also apply powdered activated carbon to help reduce taste and odor compounds as well as certain organic contaminants.

Disinfection relies on a combination of methods across the various utilities. Ozone is used at some facilities for powerful primary disinfection, while free chlorine and chloramine-based disinfection are used to maintain a protective residual throughout the distribution pipes all the way to your faucet. This residual is what prevents bacterial regrowth as water travels through miles of underground mains.

Additional treatment steps documented across the local utilities include biological treatment, aeration, and deep well disinfection for groundwater sources. The range of technologies reflects the diversity of source waters, from imported surface water to local groundwater, that feed into San Diego's overall supply.

What's in San Diego Tap Water?

The most notable finding is lithium. EPA testing found lithium at levels up to 42.6 micrograms per liter in San Diego water samples, and detections above EPA's health reference level of 10 micrograms per liter were recorded across all 41 ZIP codes in the dataset. There is no federal enforceable maximum for lithium in drinking water; the 10 micrograms per liter figure is a non-regulatory screening benchmark used to flag potential concern, not a legal limit.

Five PFAS compounds were detected in San Diego tap water: PFBA at up to 0.0089 micrograms per liter, PFOA at up to 0.0079 micrograms per liter, PFBS at up to 0.0075 micrograms per liter, and PFHxS at up to 0.0071 micrograms per liter. All four were found across all 41 tested ZIP codes. None of these individual measurements exceeded their respective EPA limits, so they do not represent a compliance violation.

Lithium in drinking water most commonly originates from natural geological sources, particularly in regions with certain mineral-bearing rock formations, though industrial and agricultural activity can also contribute. PFAS compounds in water supplies are typically traced to fire-fighting foam use, industrial discharges, and the slow migration of these persistent chemicals through soil into source water.

Health Risk Profile for San Diego

Lithium is the primary concern in San Diego's tap water. The peak detected level of 42.6 micrograms per liter is more than four times above EPA's non-regulatory health reference level of 10 micrograms per liter. Because there is no federal enforceable standard for lithium in drinking water, this is not a legal violation, but it does signal a level the EPA considers worth attention for certain populations.

Developing fetuses, infants, and pregnant individuals face the greatest potential risk from elevated lithium in drinking water. Research has associated higher lithium exposure during fetal development and early infancy with potential effects on thyroid function and neurodevelopment. People with kidney conditions may also be less able to clear lithium from the body. If you fall into one of these groups, using a filter or bottled water for drinking and formula preparation is a reasonable precaution.

For lithium, a reverse osmosis filter certified to NSF/ANSI 58 is the most effective at-home option. NSF/ANSI is an independent third-party certification standard that confirms a filter actually reduces what it claims to reduce, so look for that label on the box or product listing. Because PFAS compounds were also detected, look for a filter that also carries NSF/ANSI P473 certification, which specifically covers PFOA and PFOS removal. A system certified to both NSF/ANSI 58 and P473 would address the top concerns in this water.

The PFAS levels detected in San Diego tap water are below current EPA regulatory limits, so the immediate risk from those compounds alone is considered low under current federal standards. The science on low-level PFAS exposure and on lithium in drinking water continues to evolve, and EPA may update its guidance as research develops. Checking your utility's annual water quality report is the best way to stay current on what is actually in your local supply.