Nitrate In Drinking Water In California
What residents of California need to know about nitrate in drinking water — including how it enters water, which utilities have documented violations, and what steps to take.
Source: EPA SDWIS, State Water Resources Control Board (SWRCB), CDC · Last reviewed: 2025-01-01
Quick Answer
Is nitrate in drinking water a real concern in California?
Yes — California's Central Valley has some of the most documented agricultural nitrate contamination in the United States, affecting hundreds of thousands of residents, many in small disadvantaged communities.
Is this mostly a public-water issue, a private-well issue, or both?
Both — small public water systems drawing from shallow groundwater in the Central Valley frequently exceed the nitrate MCL, and private well users in agricultural counties face significant exposure.
What is the main reason residents should care?
Decades of intensive fertilizer application in the San Joaquin and Salinas Valleys have elevated nitrate in shallow groundwater. Many small communities in Tulare, Fresno, Kings, and Monterey Counties rely on wells that exceed the EPA's 10 mg/L nitrate limit.
Key Facts
| EPA Nitrate MCL | 10 mg/L as N (nitrate-nitrogen) |
| Primary source in CA | Agricultural fertilizer runoff in San Joaquin and Salinas Valleys |
| Public vs. well risk | Both — small public systems and private wells in agricultural zones |
| Highest-risk groups | Infants under 6 months, formula-fed babies, pregnant residents |
| State oversight | State Water Resources Control Board (SWRCB) |
Why This Matters in California
California's agricultural heartland — the San Joaquin Valley — is one of the most productive farming regions in the world. Decades of fertilizer application, irrigation return flow, and confined animal operations have elevated nitrate in the underlying groundwater. The State Water Resources Control Board has documented that hundreds of thousands of Central Valley residents, many in low-income, predominantly Latino communities, drink water exceeding the nitrate MCL of 10 mg/L as N. California has funded nitrate mitigation programs and requires water systems to report nitrate detections, but private well users in agricultural areas remain largely unprotected.
Critical — Infants Under 6 Months
Do not use tap water that exceeds 10 mg/L nitrate-nitrogen to prepare infant formula or feed infants under six months. Boiling will concentrate nitrate — do not boil. Use bottled water or a certified reverse osmosis system (NSF/ANSI 58) until the issue is resolved.
California Utilities With Nitrate Violation Records
The utilities listed below have at least one nitrate violation on record in EPA's SDWIS database. Violations may be open or resolved — see individual utility pages for current status and risk level.
City of Stockton
Stockton · 191,302 served
Victorville Water District
California · 135,983 served
Burbank-city, Water Dept.
Burbank · 105,603 served
California Water Service - San Mateo
California · 102,348 served
Hesperia Wd
California · 100,744 served
City of Tracy
Tracy · 96,609 served
City of Buena Park
Buena Park · 81,998 served
Redlands City Mud-water Div
Redlands · 78,025 served
South Gate-city, Water Dept.
South Gate · 76,443 served
Cwsc Los Altos Suburban
California · 69,973 served
How Nitrate Gets Into Drinking Water
Agricultural fertilizer and manure runoff
Nitrogen-based fertilizers and animal waste applied to California cropland can leach into groundwater or run off into surface water supplies. This is the dominant nitrate pathway in most agricultural regions.
Septic system effluent
Failing or poorly sited septic systems release nitrogen-rich wastewater near drinking water wells. Rural areas with high well density and aging septic infrastructure face elevated risk.
Concentrated animal feeding operations (CAFOs)
Large livestock facilities generate significant waste. Lagoon leaks and overapplication of manure to nearby fields can create localized nitrate hotspots in groundwater.
Natural geological deposits
In some regions, naturally occurring nitrogen compounds in soil and bedrock contribute background nitrate levels to groundwater independent of agricultural activity.
Who Should Pay Closest Attention
Families with formula-fed infants face the highest risk from nitrate above the MCL. Low-income communities and private well users in the San Joaquin and Salinas Valleys who cannot afford alternative water sources are disproportionately affected.
Households with infants under six months
Pregnant residents
Private well owners in agricultural areas
Households near livestock operations or CAFOs
Rural residents on shallow groundwater wells
Households with older or failing septic systems nearby
How to Check Your Situation in California
- 1
Identify your water utility. Use the ZIP lookup below or browse the California utility directory on this site.
- 2
Read your utility's page on this site to see its current risk level and any open nitrate violations.
- 3
Review your utility's most recent Consumer Confidence Report (CCR) — mailed annually or available on the utility's website. It must disclose any MCL exceedances.
- 4
If you are on a private well, arrange testing at a State Water Resources Control Board (SWRCB)-certified lab. Your state health department maintains a list of certified labs. Annual testing is recommended in agricultural areas.
- 5
If you have an infant under six months, use bottled water or a certified RO system (NSF/ANSI 58) immediately as a precautionary measure — do not wait for test results if you are in a high-risk area.
- 6
If your utility issues a nitrate exceedance notice, follow their guidance and do not use tap water for infants until the issue is resolved.
Treatment Options
Carbon filters and boiling do not remove nitrate. Only the options below are effective.
NSF/ANSI Standard 58 — Reverse Osmosis
RO systems certified to NSF/ANSI 58 reduce nitrate by 85–95% at the point of use. Under-sink installation required. The most practical residential option for nitrate concerns.
Distillation
Distillation units effectively remove nitrate along with most other dissolved contaminants. Suitable for drinking and cooking water — not whole-house use.
Anion Exchange
Ion exchange systems designed for nitrate removal exchange nitrate ions for chloride on a resin bed. Effective as a point-of-entry system; requires periodic regeneration and monitoring.
Carbon filters do NOT remove nitrate
Standard pitcher filters, faucet filters, and under-sink carbon units — including those certified NSF/ANSI 42 or 53 — do not remove nitrate. Do not use these for nitrate reduction.
Frequently Asked Questions
Related Pages
Nitrate — National Overview
All U.S. utilities with nitrate records
California State Overview
All utilities and water quality data
Lead in Drinking Water
A separate but common concern
Reverse Osmosis Guide
Removes 85–95% of nitrate
Well Water Guide
Private well testing and safety
All Contaminants
Complete reference library
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
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State Water Resources Control Board (SWRCB) ↗