Fresno County, CA
These figures come from wells tested in Fresno County, CA, not from any one well.
- Manganese is common in wells in Fresno County, CA (19 of 105 tested wells were over that level), so it's worth testing for.
- Sulfate is common in wells in Fresno County, CA (466 of 624 tested wells were over that level), so it's worth testing for.
- Iron is not common in wells in Fresno County, CA (5 of 107 tested wells were over). Only a test tells you about your own well.
- Wells in Fresno County, CA are typically very hard (623 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:
- manganese (common in wells here)
- sulfate (common in wells here)
- iron
- hardness
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 | 4.7% |
| Wells over the level / wells judged | 5 of 107 |
| Median | < DL mg/L |
| Years sampled | 1958–2024 |
| Wells | 111 |
| Test results | 425 |
| Wells left out | 369 |
| Sources | USGS (255) |
More than half the wells had results below the lab's detection limit, so the median is reported as below that limit.
Manganese Recent
| Level it's compared with | 0.05 mg/L |
|---|---|
| Share of wells over the level | 18% |
| Wells over the level / wells judged | 19 of 105 |
| Median | 0.0013 mg/L |
| Years sampled | 1979–2024 |
| Wells | 111 |
| Test results | 410 |
| Wells left out | 354 |
| Sources | USGS (245) |
Hardness Recent
| Level it's compared with | none; hardness is shown in bands |
|---|---|
| Share of wells very hard | 75% |
| Median | 350 mg/L as CaCO₃ |
| Years sampled | 1937–2024 |
| Wells | 623 |
| Test results | 818 |
| Wells left out | 831 |
| Sources | USGS (623) |
Sulfate Recent
| Level it's compared with | 250 mg/L |
|---|---|
| Share of wells over the level | 75% |
| Wells over the level / wells judged | 466 of 624 |
| Median | 585 mg/L |
| Years sampled | 1937–2024 |
| Wells | 624 |
| Test results | 815 |
| Wells left out | 825 |
| Sources | USGS (624) |