Illinois Well Water
Last reviewed October 29, 2026
Overview
Private wells supply water to many Illinois households. Because they are generally not regulated like public systems under the federal Safe Drinking Water Act, testing and wellhead protection are the owner’s responsibility.
Hydrogeology & what it means
Illinois uses shallow glacial-drift aquifers and deep sandstone/bedrock aquifers. The documented regional concerns below indicate what is worth testing for — not what any individual well contains.
Documented regional concerns
- Nitrate from agricultural and septic influence, especially in farmed areas.
- Naturally occurring arsenic in parts of the state — odorless and tasteless, so only testing reveals it.
- Naturally occurring radium/radionuclides in some deep aquifers.
- Hard water from carbonate (limestone/dolomite) aquifers.
- Iron and manganese causing staining and metallic taste (aesthetic).
These are documented possibilities, not a reading of your well
Frequently asked questions
What should well owners in Illinois test for?
A practical panel for Illinois private wells includes Total coliform bacteria, Nitrate (as N), pH, Arsenic, Radium / gross alpha, Total hardness, Iron, Manganese. Test bacteria and nitrate at least annually and use a state-certified laboratory; confirm local recommendations with your state health department and University of Illinois Cooperative Extension.
Are private wells regulated in Illinois?
Private wells are generally not covered by the federal Safe Drinking Water Act, though Illinois or local rules may apply to construction, permitting, or testing. Public-system limits such as EPA MCLs are useful reference points, not automatic legal limits for your well.