Groundwater in Napa County contains manganese, radon, arsenic, boron, chloride, fluoride, lead, nitrate, and PFOA and PFOS. Several of these contaminants exceed EPA health standards, which means well owners should test their water and understand what is present in their specific wells.
The rock and soil here naturally release manganese, arsenic, and radon into groundwater. Human activities add to this: agriculture contributes nitrate through fertilizer, and urban and industrial areas contribute chloride, fluoride, lead, and other chemicals. Boron appears naturally in some rock layers and also comes from industrial sources.
Groundwater in this county is moderately hard and carries elevated sodium as its main mineral character. The underlying rock dissolves slowly and releases these dissolved solids into the water. These characteristics are common across wells throughout the county, though individual wells vary.
Wells in Napa County commonly have several contaminants above EPA health standards. Arsenic, lead, and radium can damage kidneys and bones and increase cancer risk with long-term exposure. Nitrate, boron, and the chemicals PFOA and PFOS can harm child development and the immune system. Fluoride at high levels can affect bone health. Radon is a radioactive gas that increases lung cancer risk when breathed in over time.
The mineral content in county wells creates everyday quality-of-life issues. Iron and manganese stain laundry, dishes, and fixtures with yellow, brown, or black marks that are hard to remove. Moderately hard water leaves scale buildup in pipes and on fixtures, and it makes soap work less well for cleaning and bathing. This mineral buildup can shorten the lifespan of water heaters and dishwashers.
Testing is the only way to know what is actually in your well, since every well in the county is different. We recommend a comprehensive panel that checks for metals, minerals, and all the contaminants found in this area--this typically costs between two hundred and four hundred dollars. Treatment options like activated carbon filters or reverse osmosis systems can address many of these concerns, depending on what your test results show.
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 ⓘ |
|---|---|---|---|---|---|
| Manganese | 82 | 62% | Moderate | High | |
| Radon | 25 | 56% | Moderate | High ⓘ | |
| Iron | 84 | 23% | Moderate | High | |
| Arsenic | 84 | 23% | Moderate | High | |
| Fluoride | 84 | 11% | Moderate | Moderate | |
| Boron | 24 | 8% | Moderate | Moderate | |
| Chloride | 86 | 3% | Moderate |
Moderate
Elevated concentration, not % above limit
|
|
| PFOS ⓘ municipal | 32 | 3% | Moderate |
Moderate
Elevated concentration, not % above limit
|
|
| PFOA ⓘ municipal | 32 | 3% | Moderate |
Moderate
Elevated concentration, not % above limit
|
|
| Lead | 57 | 2% | Moderate | Low | |
| Nitrate | 76 | 1% | Moderate | Low | |
| Uranium | 69 | 0% | Moderate | Low | |
| Chromium (total) | 24 | 0% | Moderate | Low | |
| 1,2,3-Trichloropropane | 27 | 0% | Moderate | Safe | |
| PFHxS ⓘ municipal | 30 | 0% | Moderate | Safe | |
| PFNA ⓘ municipal | 32 | 0% | Moderate | Safe | |
| HFPO-DA (GenX) ⓘ municipal | 31 | 0% | Moderate | Safe | |
| Nitrite | 76 | 0% | Moderate | Low | |
| Perchlorate | 27 | 0% | Moderate | Low | |
| Sulfate | 84 | 0% | Moderate | Low | |
| Tds | 24 | — | Moderate | Low | |
| Hardness | 86 | — | Moderate | Low | |
| Sodium | 84 | — | Moderate | Low | |
| pH | 90 | — | Moderate | Low | |
| PFBS ⓘ municipal | 32 | — | Moderate | Safe |
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.
Loading recent water news…