Well Water in California
Contaminant risks, testing requirements, and treatment recommendations for private well owners in California.
California Geology and Groundwater
California sits on Central Valley alluvium and coastal basins. This geology directly determines what contaminants are likely in private well water. Based on this geology, California well owners face elevated risk for arsenic from natural bedrock, nitrate from agricultural activity, PFAS from industrial/military sites. Moderate risk exists for radon, uranium.
Contaminant Risk Profile
| Contaminant | Risk Level | Why |
|---|---|---|
| Arsenic | Elevated risk | Natural occurrence in bedrock. Carcinogen with no safe level. EPA MCL: 10 ppb. |
| Nitrate | Elevated risk | Agricultural runoff and septic systems. Dangerous for infants. EPA MCL: 10 mg/L. |
| Radon | Moderate risk | Some bedrock types in this state produce radon. |
| PFAS | Elevated risk | Military bases, industrial sites, or manufacturing in this state have contaminated groundwater. |
| Iron/Manganese | Moderate risk | Found in some wells depending on local geology. |
| Uranium | Moderate risk | Some geological zones may have elevated levels. |
| Fluoride | Moderate risk | Some wells may have naturally elevated levels. |
How California Compares: Municipal Water Data
CheckMyTap tracks water quality for 87 cities in California. While these numbers reflect municipal water (not private wells), they indicate the baseline mineral content of California's water sources. Private wells often draw from the same aquifers but with less treatment.
| Metric | California Average | National Average |
|---|---|---|
| Hardness | 180 PPM (very hard) | 170 PPM |
| Hardness range | 18 - 300 PPM | 25 - 400+ PPM |
| Lead (avg municipal) | 3.1 ppb | 3.2 ppb |
| Nitrate (avg municipal) | 2.4 mg/L | 1.1 mg/L |
| Cities with PFAS detected | 43 of 87 | ~45% nationally |
| Cities exceeding PFAS MCL (4 ppt) | 43 |
Hardest water in California: Encinitas (300 PPM), Camarillo (280 PPM), Rancho Cucamonga South (280 PPM), Irvine South (280 PPM), Lake Forest (280 PPM).
Softest water: Sacramento (18 PPM), San Francisco (21 PPM), Santa Cruz (28 PPM).
Testing Requirements in California
California does not have a statewide mandatory testing requirement for existing private wells. Regardless of state requirements, the EPA recommends testing annually for:
- Every year: Total coliform bacteria, E. coli, nitrate, pH, and total dissolved solids
- At least once: Arsenic, lead, copper, fluoride, and any contaminant identified as a local risk
- Recommended for California: Radon in water (granitic bedrock states have higher risk)
- Recommended for California: PFAS panel, especially if near military bases or industrial sites
- Recommended for California: Uranium, especially in areas with granitic or metamorphic bedrock
- After events: Retest after flooding, well repairs, nearby construction, or any change in taste/color/odor
Recommended Treatment for California Wells
Based on California's geology and common contaminant risks, these treatment systems address the most likely issues:
Removes arsenic, uranium, and most dissolved contaminants from drinking water
Learn moreCalifornia groundwater averages 180 PPM. A softener prevents scale damage, reduces energy waste, and extends appliance life
Learn moreKills bacteria and viruses without chemicals. Recommended for all well water systems
Frequently Asked Questions
Is well water in California safe to drink?
Well water quality in California varies significantly by location and geology. California sits on Central Valley alluvium and coastal basins. Key concerns include arsenic from natural bedrock, nitrate from agricultural activity, PFAS from industrial/military sites. The only way to know your specific water quality is to test it. Use our free interpreter to understand your results.
How often should I test my well water in California?
The EPA recommends testing annually for bacteria (total coliform, E. coli), nitrate, total dissolved solids, and pH. Given California's arsenic risk, test for arsenic at least once and after any changes to your well. Radon testing is also recommended in California. Test more frequently if you notice changes in taste, color, or odor, or after flooding, nearby construction, or well repairs.
Does California require well water testing?
California does not have a statewide mandatory testing requirement for existing private wells. However, the EPA strongly recommends annual testing regardless of state requirements. Your county health department may have additional local requirements.
What is the average water hardness in California?
Municipal water in California averages 180 PPM across 87 cities tracked by CheckMyTap, ranging from 18 to 300 PPM. Private well water typically runs 20-50% harder than city water because groundwater has more contact time with mineral formations. Most California well owners benefit from a water softener. Check your city's data.