Private wells and nitrate: testing, health risks and California help

The short answer

• You are the one who tests. Drinking water rules cover public water systems, not private wells. Test your well for nitrate and bacteria at least once a year at a state-accredited laboratory.
• Know the limit and its units. The limit is 10 mg/L measured as nitrogen (N), the same as 45 mg/L measured as nitrate (NO3). Compare your result with the number in the same units.
• At or above the limit, do not drink the water, cook with it or mix baby formula with it. Do not boil it: boiling does not remove nitrate and can concentrate it. Bathing and showering are fine.
• Use bottled or other safe water, especially for babies and during pregnancy, until you have a fix. Home treatment that works is reverse osmosis or anion exchange, certified and, in California, registered for nitrate.
• In the Central Valley, free help exists. Local groups under the Nitrate Control Program offer eligible households free well tests and free bottled water. Start with the Find Your Management Zone map.

Bring the printable private well owner checklist when you call a lab or program. This page is general information; ask your clinician or your baby's clinician what water is right for your family.

Why nitrate matters

Nitrate is a form of nitrogen. In groundwater it comes mostly from fertilizer, septic systems and animal operations such as dairies. You cannot see, smell or taste it, so only a test tells you your level.

The limit. Federal and California limits are the same: 10 mg/L of nitrate as nitrogen. Some labs and older reports give the weight of nitrate itself, and on that scale the limit is 45 mg/L. Nitrite, a related chemical, has a limit of 1 mg/L as nitrogen. California's Public Health Goal for nitrate, based on protecting infants, equals the limit.

Babies under 6 months are at greatest risk. In a young baby's stomach, nitrate turns into nitrite, which makes it harder for the blood to carry oxygen. This is methemoglobinemia, or "blue baby syndrome." Signs include shortness of breath and bluish skin, especially around the eyes and mouth. State water officials say babies with these signs need immediate medical care, because the condition can lead to coma and death. State guidance singles out infant formula made with high-nitrate water.

Pregnancy. California's health guidance names pregnant women, with infants under 6 months, as the groups at greatest risk, because high nitrate can also affect a pregnant person's blood. If you are pregnant, ask your clinician about your water, and drink water you know is below the limit.

Long-term exposure. The State Water Board notes that some studies have suggested links between high nitrate in drinking water and birth defects and certain cancers, and that longer-term research is needed to show whether nitrate causes them. The evidence is unsettled; the limit is set to prevent the harm to babies that is well established.

Skin contact is not the concern. Nitrate matters only when swallowed. California's fact sheet says it is not absorbed through the skin, so bathing and showering are fine, and washing produce is generally fine if you wipe or blot it dry.

Why a private well is different

Public water systems must test on a schedule, notify customers about problems and send a yearly water quality report. A private well has none of this. The U.S. Environmental Protection Agency (EPA) says private wells are not regulated under the federal Safe Drinking Water Act, and owners are responsible for their water. In California, wells serving one home or up to four connections are permitted by counties but not regulated by the state. If you pay a water bill, see How to find and read your water quality report instead.

Renters (California). Under a 2024 law known as AB 2454, a landlord whose rental uses a private well must test through a free program funded or regulated by the State or a Regional Water Board, where one covers the area. The landlord must share results with residents within 10 days and, if the water fails a standard and the program offers free replacement water, provide safe drinking water, without raising rent or adding fees.

Levels change. Heavy rain can carry nitrate down toward groundwater. EPA advises testing right away after flooding, nearby construction or other big changes near the well.

How to test your well for nitrate

When. EPA and the State Water Board recommend testing at least yearly for nitrate and total coliform bacteria; the Board adds electrical conductivity, a measure of dissolved salts. EPA advises testing more often if young children or older adults live with you, or someone is pregnant or nursing.

Who. EPA says to use a laboratory certified for drinking water testing. In California, the State Water Board's Environmental Laboratory Accreditation Program (ELAP) lists accredited labs. A store-bought kit can show whether nitrate is present but may not give a number; a certified lab measures how much. In much of the Central Valley, a free program may test for you; check that first (see "California help").

Cost. The State Water Board's well owner guide (June 2025) lists a typical nitrate test at $25 to $60, and its testing page says a basic package of several tests can run $100 to $400. Ask for a written estimate.

What to ask for:

• Nitrate and nitrite, with nitrate reported as nitrogen (N)
• Total coliform bacteria and electrical conductivity
• Anything common near you. Self-Help Enterprises lists arsenic, uranium, the pesticide DBCP and 1,2,3-trichloropropane (TCP), along with nitrate and bacteria, as common in much of Fresno, Tulare, Kings and Kern counties.

How to sample. Call the lab first and use its clean bottles. Sample as close to the well as you can, from a spigot near the wellhead if there is one, and before any filter or treatment device. Follow the lab's instructions for storing the sample and returning it on time, and note the date and tap.

Reading your result

Check the units on the nitrate line before you compare.

• Below the limit: the water meets the nitrate standard. Keep testing yearly and watch for a rising trend.
• At or above the limit: treat the water as unsafe to drink. The State Water Board advises re-testing to confirm and using another drinking water source meanwhile.
• Bacteria found: a separate problem with its own fixes. Ask the lab or your county environmental health office.

What to do if nitrate is at or above the limit

• Stop using the water for drinking, cooking, ice and infant formula.
• Do not boil it. Boiling does not remove nitrate; as water boils off, nitrate becomes more concentrated.
• Use bottled or other safe water, first for babies and anyone pregnant, and ideally for everyone.
• Keep bathing, showering, handwashing and laundry as usual.

Filters that will not do it. A pitcher, faucet or refrigerator filter does not remove nitrate unless its certification lists nitrate. In the listings of NSF, a major independent certifier, nitrate reduction appears only under the reverse osmosis standard, not the filter standards NSF/ANSI 42 and 53.

In California, check registration. Treatment devices sold with a health claim, such as nitrate reduction, must be registered with the State Water Board, which requires proof of independent certification and keeps a list of registered devices. A device's Performance Data Sheet shows what it is certified to reduce. The Board says home treatment generally suits nitrate up to 24 mg/L as nitrogen and needs water pressure of at least 40 psi. Replace filters on schedule, and have the treated water lab-tested regularly.

California help

Central Valley: free well tests and bottled water

The Central Valley Regional Water Quality Control Board adopted a Nitrate Control Program in 2018, with state approvals in 2019 and 2020. Under it, many farms, dairies and other permitted businesses that discharge nitrate have joined local groups called management zones. CV-SALTS, the Valley's salt and nitrate coalition, says the zones find high-nitrate areas, offer residents well-water testing, deliver free bottled water to households whose wells exceed the limit, and work on long-term solutions. Some zones also test for other contaminants with state funding.

Use the CV-SALTS map to see whether your home qualifies. CV-SALTS notes that if you or your landlord pays a monthly water bill, you are likely on a public system and not covered.

Kings Water Alliance, step by step. Check your address on its map and fill out a short survey online or on paper; call (559) 549-6747 for a paper copy with a prepaid envelope. If you are eligible, staff sample water at your well, without entering your home, and send it to a certified lab. If nitrate is above the safe level, the household gets free bottled water every two weeks.

Self-Help Enterprises

This nonprofit offers free programs, for people who qualify by income, to check a well's condition, test water through state-accredited labs, install a filtration system at a tap or for the whole house if testing finds a problem, and deliver bottled water meanwhile. Call 559-802-1285 (water quality) or 559-802-1284 (bottled water).

Statewide: SAFER and county programs

California's SAFER program (Safe and Affordable Funding for Equity and Resilience), whose fund was created by a 2019 law, pays for county and regional programs that can offer well testing, home treatment, well repair or replacement, connection to a public system, and hauled, vended or bottled water. The State Water Board's AB 2454 page links a county-by-county directory of state-funded well programs, updated June 2026. Not every program offers free replacement water.

Fresno County Environmental Health

County environmental health offices may help you understand results and advise on well problems. In Fresno County, the Department of Public Health's Environmental Health Division lists its Water Surveillance Program office at 1221 Fulton Street, 3rd Floor, Fresno, phone (559) 600-3357. Its well topics include how to interpret a bacteriological or chemical analysis report.

The decisions behind your well water

How much nitrate reaches groundwater, and how far water levels fall, are decided in public processes you can join.

• The Nitrate Control Program. The Central Valley Water Board posts management zone plans, notices in English and Spanish, comment letters and its responses on its management zone page. For example, the newest zones' proposals were open for public comment from February 23 to March 24, 2026. You can sign up for email updates from the Board's CV-SALTS page.
• Groundwater sustainability. Under the Sustainable Groundwater Management Act of 2014, local groundwater sustainability agencies write and carry out plans for each high- and medium-priority basin. Their pumping decisions matter because household wells tend to be shallower than larger systems' wells and are more likely to go dry. The State Water Board explains how to find your local agency.

For the policy questions behind drinking water standards, see Drinking-water governance and health. If a flood watch or warning is issued where you live (what each one means), plan to re-test your well after the water recedes.

Sources

1. Nitrates and Nitrites in Drinking Water — California State Water Resources Control Board, Division of Drinking Water, page last updated April 7, 2026.
2. Nitrate Fact Sheet — California Department of Public Health, updated May 2014 (hosted by the State Water Board).
3. Groundwater Information Sheet: Nitrate — State Water Resources Control Board, GAMA Program, revised November 2017.
4. 40 CFR 141.62, Maximum contaminant levels for inorganic contaminants — Electronic Code of Federal Regulations, accessed October 26, 2026.
5. Private Drinking Water Wells and Protect Your Home's Water — U.S. Environmental Protection Agency, last updated August 25, 2026, and February 26, 2026.
6. A Guide for Private Domestic Well Owners — State Water Resources Control Board, GAMA Program, June 2025.
7. GAMA – Domestic Well Testing — State Water Resources Control Board, page last updated September 15, 2023.
8. Environmental Laboratory Accreditation Program (ELAP) — State Water Resources Control Board, page last updated October 20, 2026.
9. Residential Water Treatment Devices and List of Registered Devices — State Water Resources Control Board, Division of Drinking Water, page last updated June 27, 2025.
10. NSF/ANSI 58: Reverse Osmosis Drinking Water Treatment Systems — NSF, December 18, 2025.
11. NSF Standards for Water Treatment Systems and certified drinking water treatment unit listings — NSF, accessed October 26, 2026.
12. Rental Property Domestic Well Testing Requirements (AB 2454) and its Well Testing Program Directory — State Water Resources Control Board, directory last updated June 2026.
13. SAFER Drinking Water, page last updated October 26, 2026, and Strategy for State Small Water Systems, Domestic Wells and Other Self-Supplied Communities — State Water Resources Control Board, accessed October 26, 2026.
14. Nitrate Program, Management Zones, Residential Well Testing and Find Your Management Zone — CV-SALTS, Central Valley Salinity Coalition, accessed October 26, 2026.
15. CV-SALTS and Nitrate Control Program management zones — Central Valley Regional Water Quality Control Board, page last updated August 21, 2026, and accessed October 26, 2026.
16. Free Well Testing & Bottled Water Delivery: How to Get Started and home page — Kings Water Alliance, accessed October 26, 2026.
17. Tule Basin Water Foundation, Kern Water Collaborative, Kaweah Water Foundation and Chowchilla Management Zone — management zone organizations, accessed October 26, 2026.
18. Water Quality and Safe Drinking Water — Self-Help Enterprises, accessed October 26, 2026.
19. Water Surveillance Program — Fresno County Department of Public Health, Environmental Health Division, accessed October 26, 2026.
20. About SGMA — State Water Resources Control Board, accessed October 26, 2026.