Sonoma County groundwater contains radon, manganese, iron, arsenic, boron, chloride, fluoride, nitrate, PFOA, PFOS, and sulfate at levels that exceed EPA health standards. These contaminants appear at concerning levels across the county and warrant testing of individual wells.
These contaminants come from a mix of sources in the local rock and human activity. Radon, arsenic, and metals like manganese and iron occur naturally in the county's varied rock layers and are released into groundwater as it moves through the ground. Nitrate, chloride, PFOA, and PFOS come from fertilizer use, road salt, and industrial chemicals that seep down from the surface. Boron and fluoride also occur naturally in some rock types in this region.
Groundwater in Sonoma County is moderately hard, driven mainly by calcium and magnesium from the local rock below. The county's varied geology creates water with moderate hardness and elevated total dissolved solids, meaning more minerals are dissolved in the water overall. Most wells across the county show these moderately hard characteristics, though individual wells can vary.
Wells in Sonoma County have been found to exceed EPA health standards for arsenic, boron, fluoride, nitrate, PFOA, PFOS, radon, and manganese. Arsenic is a poison that builds up in your body over time and raises cancer risk. Radon is a radioactive gas that damages your lungs. Nitrate harms infants and can cause serious illness. PFOA and PFOS are toxic chemicals that affect your liver and immune system. Boron, fluoride, and manganese can cause bone and nervous system problems with long-term exposure.
County wells also contain minerals that affect daily life. The water is moderately hard, which means you will see white scale on faucets and showerheads, inside kettles, and on dishes. Scale builds up inside water heaters and dishwashers and can shorten how long they last. You may notice staining on sinks and tubs from iron and manganese.
We recommend a comprehensive water test right away because your well is different from others in the county--it could have higher or lower levels of these contaminants. Testing is the only way to know what is actually in your water so you can treat it correctly. A comprehensive panel costs two hundred to four hundred dollars. Treatment options include reverse osmosis filters, activated carbon, or whole-house systems depending on what your test shows.
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 ⓘ |
|---|---|---|---|---|---|
| Radon | 60 | 52% | Moderate | High ⓘ | |
| Manganese | 218 | 36% | High | High | |
| Iron | 361 | 11% | High | Moderate | |
| Arsenic | 249 | 8% | High | Moderate | |
| Boron | 67 | 6% | Moderate | Moderate | |
| PFOS ⓘ municipal | 115 | 2% | High | Low | |
| PFOA ⓘ municipal | 115 | 2% | High | Low | |
| Fluoride | 358 | 1% | High | Low | |
| Chloride | 366 | 1% | High | Low | |
| Nitrate | 218 | 1% | High | Low | |
| Sulfate | 361 | 1% | High | Low | |
| Nitrite | 217 | 0% | High | Low | |
| HFPO-DA (GenX) ⓘ municipal | 114 | 0% | High | Safe | |
| Perchlorate | 69 | 0% | Moderate | Low | |
| Uranium | 185 | 0% | High | Low | |
| PFNA ⓘ municipal | 115 | 0% | High | Safe | |
| Chromium (total) | 69 | 0% | Moderate | Low | |
| 1,2,3-Trichloropropane | 69 | 0% | Moderate | Safe | |
| Lead | 211 | 0% | High | Low | |
| PFHxS ⓘ municipal | 115 | 0% | High | Low | |
| Tds | 68 | — | Moderate | Low | |
| Sodium | 365 | — | High | Low | |
| Hardness | 366 | — | High | Low | |
| PFBS ⓘ municipal | 115 | — | High | Low | |
| pH | 372 | — | 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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