Fresno County groundwater contains arsenic, boron, chloride, fluoride, lead, manganese, nitrate, radon, sulfate, uranium, and industrial compounds like PFOA and trichloropropane. Many of these contaminants exceed EPA health standards, making them a serious concern for well owners in this county.
The Central Valley sits atop ancient lake beds and river deposits that naturally contain dissolved salts and minerals. Over time, agricultural activity--fertilizer runoff and irrigation--has added nitrate and other chemicals to the groundwater. Some contaminants like arsenic and uranium occur naturally in the rock layers here, while others like PFOA come from industrial use and firefighting foam.
Groundwater in this county is very hard and carries extremely high levels of sodium and sulfate from the minerals in these sedimentary deposits. The rock and soil layers underground release these salts into water moving through them. These characteristics are widespread across wells throughout Fresno County.
Wells in Fresno County commonly have arsenic, boron, lead, uranium, and radon above EPA health limits. Arsenic and uranium can damage kidneys and increase cancer risk. Lead harms children's brain development and learning. Boron affects reproduction and development in fetuses and young children. Radon is a radioactive gas that causes lung cancer. Nitrate, nitrite, and certain industrial chemicals in some county wells can poison blood and interfere with oxygen transport in infants and children.
County well water is extremely hard and very salty. The high mineral content leaves white scale on faucets, fixtures, and inside pipes. It stains laundry and makes soap work poorly. The water tastes salty and bitter. Hard water shortens the life of water heaters, dishwashers, and washing machines because minerals build up inside them.
We recommend testing your well with a comprehensive panel to find out exactly what is in your water. Every well is different--yours could have much higher or much lower levels than what is common across the county. Testing is the only way to know what you are drinking and what needs treatment. A comprehensive metals and minerals panel costs between two hundred and four hundred dollars. Depending on what testing shows, treatment options include reverse osmosis systems, activated carbon filters, or specialized filters for specific contaminants.
Not sure if your well is affected? Get certified results in 5–7 days.
Test Your Well Water with Tap Score →| Contaminant | Samples ⓘ | % Above MCL ⓘ | Distribution ⓘ | Confidence ⓘ | Risk ⓘ |
|---|---|---|---|---|---|
| Sulfate | 2078 | 68% | High | High | |
| Radon | 117 | 43% | High | High ⓘ | |
| Nitrate | 1438 | 37% | High | High | |
| Chloride | 2081 | 34% | High | High | |
| 1,2,3-Trichloropropane | 60 | 27% | Moderate | High | |
| Uranium | 374 | 24% | High | High | |
| Manganese | 1119 | 17% | High | High | |
| Boron | 60 | 12% | Moderate | Moderate | |
| PFOS ⓘ municipal | 575 | 10% | High | Moderate | |
| PFOA ⓘ municipal | 575 | 9% | High | Moderate | |
| Iron | 1145 | 5% | High | Moderate | |
| Arsenic | 875 | 4% | High |
Moderate
Elevated concentration, not % above limit
|
|
| Nitrite | 995 | 1% | High | Low | |
| PFHxS ⓘ municipal | 575 | 1% | High | Low | |
| Lead | 624 | 1% | High | Low | |
| Fluoride | 1160 | 0% | High | Low | |
| HFPO-DA (GenX) ⓘ municipal | 569 | 0% | High | Safe | |
| Perchlorate | 56 | 0% | Moderate | Low | |
| PFNA ⓘ municipal | 575 | 0% | High | Low | |
| Chromium (total) | 60 | 0% | Moderate | Low | |
| Tds | 60 | — | Moderate | Low | |
| Hardness | 2080 | — | High | Low | |
| PFBS ⓘ municipal | 575 | — | High | Low | |
| Sodium | 2098 | — | High | Low | |
| pH | 2430 | — | High | Low |
MCL = Maximum Contaminant Level (EPA limit for public water; used as benchmark for private wells). Distribution shows % of sampled wells in each concentration band. Methodology.
* Microbial contaminants (E. coli, coliform) reflect only samples from the last 10 years.
Data shows potential risk — a certified test confirms whether your water is affected.
Order a Tap Score Test →Population-level CDC data. Not individual risk prediction.
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