How Often Should You Test Your Well Water in Illinois?
August 2026 · 3 min read
Unlike a municipal water supply that's continuously monitored, a private well is only as current as the last time it was tested — which makes the testing schedule itself part of keeping your water safe.
The baseline: annually for bacteria
The Illinois Department of Public Health recommends testing private well water for bacteria at least once a year. Bacterial contamination can develop without any visible or noticeable change in taste, smell, or clarity, which is exactly why an annual test matters even when nothing seems different.
Minerals and other contaminants: every few years, or when something changes
Hardness, iron, sulfur, and nitrates don't need annual testing at the same frequency as bacteria, but should be checked every few years, and immediately if you notice a change — new staining, a new odor, a taste change, or a shift in water pressure. Homes near agricultural land should also test for nitrates periodically, since agricultural runoff can affect groundwater over time.
Test sooner if:
- You just moved into a home with a well and don't have recent test results.
- There's been flooding or heavy construction near your well.
- A household member is pregnant, an infant, or otherwise more vulnerable to contaminants.
- You've had well or plumbing repair work done recently.
Where to get a comprehensive test
A licensed water treatment contractor can run a comprehensive panel — bacteria, hardness, iron, sulfur, pH, and nitrates — as part of a free in-home assessment, giving you both a safety check and the data needed to size any treatment system correctly.