California tap water quality: the plain-English guide

Is California tap water safe to drink?

For most Californians the honest answer is: your tap water almost certainly comes from a regulated public water system that must test on a fixed schedule, report the results to the State Water Resources Control Board, and mail or post an annual Consumer Confidence Report (CCR). Systems that exceed a legal limit must notify customers. That framework is strong, but "legal" is not the same thing as "ideal," and the state is large enough that water quality varies a lot from one utility to the next.

California sets two kinds of numbers. A Maximum Contaminant Level (MCL) is the enforceable legal limit. A Public Health Goal (PHG), set by the Office of Environmental Health Hazard Assessment (OEHHA PHG list), is the level at which no significant health risk is expected over a lifetime. PHGs are not enforceable and are often far below the MCL. When a TapCheck report shows a detection that is under the MCL but above the PHG, that is not a violation; it is the gap many homeowners want to understand before deciding whether a home filter is worth it.

Water systems in California also deal with a few issues that national guides tend to skip: very hard imported water across much of Southern California, naturally occurring chromium 6 and arsenic in groundwater, nitrate from agriculture in farm regions, and PFAS ("forever chemicals") that the state now tracks with notification and response levels. Each of those has its own guide below.

California water quality guides

Other contaminants Californians ask about

Arsenic. Arsenic occurs naturally in some California groundwater. The state MCL is 10 µg/L (0.010 mg/L), and the state water board has a page on arsenic in drinking water including its review of the MCL. Public systems test for it; private well owners must test on their own.

Nitrate. Nitrate is mostly linked to fertilizer, dairies and septic systems, so it shows up most in farm-region groundwater. The MCL is 10 mg/L as nitrogen and it is especially important for infants. See the board's nitrate and nitrite page.

Lead. Lead usually comes from home plumbing, fixtures or service lines, not from the treatment plant. A ZIP report shows the utility's lead and copper sampling, but only a sample from your own faucet tells you about your own pipes.

Chlorine and chloramine taste. Utilities add a disinfectant so water stays safe in the pipes. Many Southern California utilities use chloramine. A taste or smell of "pool water" is usually disinfectant, not contamination. Carbon filters certified to NSF/ANSI 42 reduce chlorine taste and odor; check the product's certification for chloramine specifically.

Private wells. If you are on a private domestic well, none of the public-system data applies to you. The State Water Board's GAMA domestic well program explains testing.

Water quality by region and city

Utilities and source water change across the state, so start local:

• Inland Empire: Riverside, San Bernardino, Fontana, Rialto, Ontario, Rancho Cucamonga, Corona, Moreno Valley, Temecula
• Los Angeles: Los Angeles, Long Beach, Pasadena, Glendale, Santa Monica
• San Diego: San Diego, Chula Vista, Oceanside, Escondido
• Bay Area: San Francisco, Oakland, San Jose, Fremont
• Sacramento and Central Valley: Sacramento, Elk Grove, Roseville, Fresno, Stockton

Every city is listed on the city guides page.

Where the data comes from

TapCheck reports draw on California's public drinking water records. You can check any number yourself:

• Drinking Water Watch: the State Water Board's public portal for each system's sampling results and violations.
• Your utility's annual Consumer Confidence Report; the state explains how to find it on its My Water Quality portal, and EPA explains CCRs at epa.gov/ccr.
• OEHHA's Public Health Goals and the board's notification levels.
• The EWG Tap Water Database is an independent nonprofit view that uses its own health guidelines; TapCheck is not affiliated with EWG.

Our methodology explains how a ZIP is matched to a utility and what the report does and does not show. New to the terms? Try how to read your report and the glossary.

How to decide whether you need a filter

1. Find your utility. Run your ZIP and confirm the name against your water bill.
2. Compare each detection with the MCL and the PHG. Over the MCL is a violation and the utility must notify you. Between the PHG and the MCL is legal, but it is the range where a home filter may still reduce exposure.
3. Match the filter to the contaminant. Hardness calls for a softener or scale control. Chlorine taste calls for carbon. PFAS, chromium 6, arsenic and nitrate generally call for reverse osmosis or other systems certified for that specific contaminant.
4. Check certification. Look the product up in the NSF certified drinking water products listings for the exact contaminant claim.
5. Test at the tap if it matters. For lead, private wells or a health concern, a certified lab test of your own faucet is the only direct answer.

The filter basics page compares carbon and reverse osmosis in plain English.

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