Groundwater in Contra Costa County contains manganese, chloride, and nitrate that well owners should monitor. Several of these contaminants, including chloride, iron, manganese, nitrate, and sulfate, exceed EPA health standards in this county's water.
These contaminants come from a mix of natural and human sources. The underlying rocks release minerals like manganese and sulfate into the water over time. Chloride and nitrate enter groundwater from road salt, fertilizers, and septic systems in populated areas. Saltwater intrusion from the nearby coast also pushes chloride into some wells, especially closer to the bay.
Groundwater in Contra Costa County is very hard, driven by high levels of sodium, sulfate, and the mineral content that builds up as water moves through the rock. The complex geology here allows minerals to accumulate rather than flush through quickly. Very hard water is widespread across wells in this county.
Wells in Contra Costa County sometimes contain chloride, iron, manganese, nitrate, and sulfate at levels above EPA health standards. Nitrate can affect how blood carries oxygen, especially in babies and young children. Manganese at high levels can harm the brain and nervous system over time. Chloride itself is not directly toxic, but it indicates salty water that reflects other mineral problems.
County well water is very hard, which causes white scale buildup on faucets and fixtures. This scale clogs pipes and shortens the life of water heaters and dishwashers. You may notice rust staining on sinks and toilets from iron in the water. The high sodium content and sulfate can give the water a salty or musty taste.
We recommend testing your well water, since every well in the county is different and yours could have higher or lower levels than average. Testing is the only way to know what is actually in your water so you can treat it properly. A comprehensive metals and minerals panel typically costs between two hundred and four hundred dollars and will show you exactly what you are dealing with. Iron filters and water softeners can help reduce both the hardness and mineral problems common in this area.
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 | 80 | 58% | Moderate | High | |
| Chloride | 1191 | 39% | High | High | |
| Nitrate | 142 | 8% | High | Moderate | |
| Iron | 92 | 8% | Moderate | Moderate | |
| Sulfate | 123 | 7% | High | Moderate | |
| Lead | 15 | 0% | Moderate | Safe | |
| PFHxS ⓘ municipal | 48 | 0% | Moderate | Safe | |
| Arsenic | 9 | 0% | Low | Low ⓘ | |
| PFOA ⓘ municipal | 48 | 0% | Moderate | Safe | |
| Fluoride | 116 | 0% | High | Low | |
| HFPO-DA (GenX) ⓘ municipal | 48 | 0% | Moderate | Safe | |
| Nitrite | 71 | 0% | Moderate | Low | |
| PFOS ⓘ municipal | 48 | 0% | Moderate | Safe | |
| PFNA ⓘ municipal | 48 | 0% | Moderate | Safe | |
| pH | 270 | — | High | Low | |
| PFBS ⓘ municipal | 48 | — | Moderate | Safe | |
| Sodium | 139 | — | High | Low | |
| Hardness | 147 | — | 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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