Mendocino County, CA
These figures come from wells tested in Mendocino County, CA, not from any one well.
- Iron is common in wells in Mendocino County, CA (8 of 31 tested wells were over that level), so it's worth testing for.
- Manganese is common in wells in Mendocino County, CA (14 of 31 tested wells were over that level), so it's worth testing for.
- Sulfate is not common in wells in Mendocino County, CA (0 of 82 tested wells were over). Only a test tells you about your own well.
- Wells in Mendocino County, CA are typically hard (83 wells tested).
- Only a test of your own well tells you about your water.
What to test for
Start with the four this site covers:
- iron (common in wells here)
- manganese (common in wells here)
- hardness
- sulfate
Most well owners also test for these. We point to the source and don't interpret the results.
- arsenic: occurs naturally in groundwater in many regions. USGS: arsenic and drinking water
- nitrate: common near farmland and septic systems. EPA: private drinking water wells
- total coliform bacteria: the standard yearly well check. EPA: private drinking water wells
- lead and copper: from household plumbing, especially when pH is below 6.5. EPA: lead in drinking water
- PFAS: several states run private-well sampling programs. EPA: PFAS
- a certified lab: states certify labs and some run their own private-well programs. California's certified-lab list (from your state drinking-water program)
The numbers
County figures describe the wells sampled there, not any one well. Exact counts, sample years and sources are below.
Iron Recent
| Level it's compared with | 0.3 mg/L |
|---|---|
| Share of wells over the level | 26% |
| Wells over the level / wells judged | 8 of 31 |
| Median | 0.0383 mg/L |
| Years sampled | 1969–2025 |
| Wells | 31 |
| Test results | 120 |
| Wells left out | 57 |
| Sources | USGS (77), CWLT_WQX (3), POTTERVALLEYTRIBE (2), HOPTERA_WQX (1) |
Manganese Recent
| Level it's compared with | 0.05 mg/L |
|---|---|
| Share of wells over the level | 45% |
| Wells over the level / wells judged | 14 of 31 |
| Median | 0.0433 mg/L |
| Years sampled | 1969–2025 |
| Wells | 31 |
| Test results | 111 |
| Wells left out | 54 |
| Sources | USGS (66), CWLT_WQX (3), POTTERVALLEYTRIBE (2), HOPTERA_WQX (1) |
Hardness Recent
| Level it's compared with | none; hardness is shown in bands |
|---|---|
| Share of wells very hard | 22% |
| Median | 120 mg/L as CaCO₃ |
| Years sampled | 1965–2025 |
| Wells | 83 |
| Test results | 134 |
| Wells left out | 58 |
| Sources | USGS (77), CWLT_WQX (3), POTTERVALLEYTRIBE (2), HOPTERA_WQX (1) |
Sulfate Recent
| Level it's compared with | 250 mg/L |
|---|---|
| Share of wells over the level | 0.0% |
| Wells over the level / wells judged | 0 of 82 |
| Median | 7.515 mg/L |
| Years sampled | 1965–2025 |
| Wells | 82 |
| Test results | 130 |
| Wells left out | 58 |
| Sources | USGS (77), CWLT_WQX (3), POTTERVALLEYTRIBE (2) |