Nitrate in California Drinking Water — 235 ZIPs Tested
EPA data analysis for nitrate in California drinking water systems
Nitrate Contamination in California
ZipCheckup analyzed drinking water data across 2,630 ZIP codes in California for nitrate contamination. 235 ZIP codes have reported nitrate detections, and 136 have EPA violations on record.
The violation rate for nitrate in California is 5.2% of all ZIP codes — higher than the national average.
EPA Standard for Nitrate
The EPA maximum contaminant level (MCL) for nitrate is 10 mg/L (as nitrogen), governed by the National Primary Drinking Water Regulations. Water systems that exceed this limit must take corrective action and notify consumers.
Worst ZIP Codes for Nitrate in California
These ZIP codes reported the highest nitrate levels in California based on CCR reports and EPA data:
Lowest Nitrate Levels in California
These ZIP codes had the lowest reported nitrate detections in California:
Health Effects of Nitrate
How to Remove Nitrate From Drinking Water
The most effective treatment for nitrate removal is Reverse Osmosis or Ion Exchange. Look for filters certified under NSF 53 / NSF 58 standards.
Check Your ZIP Code
Use the ZipCheckup water quality search to see nitrate data for your specific water system in California.
Worst ZIP Codes for Nitrate in California
Ranked by highest nitrate detection level.
| Rank | ZIP Code | City | Level Detected | EPA Limit | Status |
|---|---|---|---|---|---|
| 1 | 91385 | Valencia | 29.8 ppm | 45 ppm | Within Limit |
| 2 | 95023 | Hollister | 28 ppm | 45 ppm | Within Limit |
| 3 | 95024 | Hollister | 28 ppm | 45 ppm | Within Limit |
| 4 | 91011 | La Canada Flintridge | 25 ppm as NO3 | 45 ppm as NO3 | Within Limit |
| 5 | 91012 | La Canada Flintridge | 25 ppm as NO3 | 45 ppm as NO3 | Within Limit |
| 6 | 92545 | Hemet | 25 ppm | 45 ppm | Within Limit |
| 7 | 93666 | Sultana | 23.5 ppm | 45 ppm | Within Limit |
| 8 | 95360 | Newman | 23.1 ppm | 45 ppm | Within Limit |
| 9 | 93244 | Lemon Cove | 19.5 ppm | 10 ppm | Exceeds |
| 10 | 92564 | Murrieta | 15 ppm | 10 ppm | Exceeds |
| 11 | 93650 | Fresno | 13 mg/L | 10 mg/L | Exceeds |
| 12 | 93701 | Fresno | 13 mg/L | 10 mg/L | Exceeds |
| 13 | 93702 | Fresno | 13 mg/L | 10 mg/L | Exceeds |
| 14 | 93703 | Fresno | 13 mg/L | 10 mg/L | Exceeds |
| 15 | 93704 | Fresno | 13 mg/L | 10 mg/L | Exceeds |
| 16 | 93705 | Fresno | 13 mg/L | 10 mg/L | Exceeds |
| 17 | 93706 | Fresno | 13 mg/L | 10 mg/L | Exceeds |
| 18 | 93707 | Fresno | 13 mg/L | 10 mg/L | Exceeds |
| 19 | 93708 | Fresno | 13 mg/L | 10 mg/L | Exceeds |
| 20 | 93709 | Fresno | 13 mg/L | 10 mg/L | Exceeds |
Lowest Nitrate Levels in California
Cities with Nitrate Data in California
72 cities in California have nitrate testing data available.
+ 52 more cities