Groundwater in Merced County contains arsenic, chloride, uranium, nitrate, perchlorate, radon, lead, manganese, iron, fluoride, sulfate, nitrite, and trace organic chemicals. Many of these contaminants exceed EPA health standards at levels that well owners need to address.
These contaminants come from a mix of sources in the valley. Agricultural chemicals like nitrate and perchlorate seep down from farm fields. Naturally occurring elements like arsenic and uranium dissolve from the rock layers in the underground aquifer. Salt and other minerals concentrate in groundwater where water moves slowly through the valley's thick sediment layers. Industrial activity and urban development add lead and synthetic chemicals to the water over time.
Groundwater in this county is hard, driven by elevated calcium and magnesium from the sediment and rock that water passes through. The moderate sodium levels and low sulfate reflect the valley's geology and slow-moving water. Hard water is common across wells throughout Merced County.
Wells in Merced County commonly contain arsenic, lead, uranium, radon, nitrate, and several other contaminants at levels above EPA health standards. Arsenic and uranium are linked to cancer risk with long-term exposure. Lead harms children's brain development and causes kidney damage in adults. Radon increases lung cancer risk. Nitrate and nitrite can cause serious illness in infants. Perchlorate and PFOA/PFOS chemicals affect thyroid function and immune system development.
County well water is hard, which means you probably see white scale buildup on faucets and showerheads, staining on sinks and tubs, and soap that does not lather well. Hard water shortens the life of water heaters, dishwashers, and washing machines because scale clogs pipes and reduces efficiency. You may notice a salty or mineral taste in your water.
We recommend a comprehensive water test right away because Merced County wells show multiple contaminants at health-threatening levels. Every well is different--yours could have higher or lower levels than the county average, and testing is the only way to know what is actually in your water and how to treat it. A comprehensive panel typically costs $200-400. Treatment options like reverse osmosis, activated carbon filters, or ion exchange can address different 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 ⓘ |
|---|---|---|---|---|---|
| Manganese | 669 | 24% | High | High | |
| Chloride | 1488 | 18% | High | High | |
| Uranium | 160 | 16% | High | High | |
| Sulfate | 1274 | 15% | High | High | |
| 1,2,3-Trichloropropane | 46 | 15% | Moderate | High | |
| Iron | 759 | 13% | High | Moderate | |
| Nitrate | 970 | 13% | High | Moderate | |
| PFOS ⓘ municipal | 175 | 8% | High | Moderate | |
| Arsenic | 510 | 8% | High | Moderate | |
| Radon | 27 | 4% | Moderate |
Moderate
ⓘ
Elevated concentration, not % above limit
|
|
| PFOA ⓘ municipal | 175 | 3% | High |
Moderate
Elevated concentration, not % above limit
|
|
| PFHxS ⓘ municipal | 175 | 3% | High |
Moderate
Elevated concentration, not % above limit
|
|
| Perchlorate | 46 | 2% | Moderate | Low | |
| Lead | 409 | 1% | High | Low | |
| Nitrite | 425 | 0% | High | Low | |
| Fluoride | 1020 | 0% | High | Low | |
| PFNA ⓘ municipal | 175 | 0% | High | Safe | |
| Boron | 40 | 0% | Moderate | Low | |
| Chromium (total) | 40 | 0% | Moderate | Low | |
| HFPO-DA (GenX) ⓘ municipal | 175 | 0% | High | Safe | |
| Tds | 40 | — | Moderate | Low | |
| pH | 40 | — | Moderate | Low | |
| Sodium | 1491 | — | High | Low | |
| Hardness | 1450 | — | High | Low | |
| Total Coliform | 34* | 0% | Moderate | Low | |
| PFBS ⓘ municipal | 175 | — | High | Low | |
| E. coli | 34* | 0% | 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.
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