Cook County, Illinois has about 5,182,617 residents (Census 2024 estimate) and 163 community water systems in EPA records. The largest local system is Chicago, serving about 2,721,308 people from surface water.
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
Chicago No data: see your utility report · No data
No reliable figure. Test your water.
Chicago treats Lake Michigan water (2025 Water Quality Report), not local streams or wells. Local stream and well samples don't reflect this water, so we don't show a county estimate. Check the utility's annual water quality report or test your water.
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
At this hardness most homes don't need a softener. Confirm with a test strip if you see scale.
The 6 biggest of 163 community water systems on EPA records for this county. Service areas don't follow county lines; your water bill names your provider.
IL0316000 · serves about 2,721,308 people · Surface water
Lead 90th percentile: 6.4 ppb (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
IL0310510 · serves about 83,000 people · Surface water
Lead 90th percentile: 5 ppb (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
IL0314890 · serves about 75,750 people · Surface water
Lead 90th percentile: 1.4 ppb (period starting 2025-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
IL0310810 · serves about 74,486 people · Surface water
Lead 90th percentile: 6.5 ppb (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
IL0314030 · serves about 73,320 people · Surface water
Lead 90th percentile: 7.6 ppb (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
IL0312340 · serves about 70,875 people · Surface water
Lead 90th percentile: 8.9 ppb (period starting 2026-01-01). Action level: 15 ppb (drops to 10 ppb on Nov 1, 2027).
Public-record figures, not a test of your tap. Not 100% accurate or guaranteed. Confirm with a water test, your utility or a qualified pro before you buy or act.
A PFAS detection is not a violation. Federal limits (4 ppt for PFOA and PFOS) apply to running annual averages, with compliance required by 2029. In May 2026 EPA proposed extending the PFOA/PFOS deadline to 2031 and removing other PFAS limits; not final as of 2026-10-21.
These are public records for whole systems. Your home's pipes, fixtures and any private well can change what you drink. A certified lab test or a hardness test strip gives you your own numbers. Then use our PFAS and lead filter selector to see which certifications to look for.
1 of the 6 largest systems here have at least one health-based violation in EPA records since October 2021 (see each system below for status). Chicago's most recent lead 90th percentile was 6.4 ppb (2026), below the 15 ppb action level. Public records can't guarantee what comes out of your tap, especially with older plumbing, so a home test is the surest check.
We don't have a reliable hardness figure for Chicago, so test your water or check its annual water quality report.
None of the 6 sampled systems listed here detected PFAS above EPA's reporting levels in UCMR 5 testing.
Most homes are served by Chicago or one of the other systems listed on this page, but service areas don't follow county lines. Your water bill names your provider, and its annual Consumer Confidence Report has the full test results.
Data as of October 21, 2026. Figures are copied from public records and combined with our own calculations; they can be out of date or wrong. Tapped Out isn't affiliated with any utility or the EPA. Written and reviewed by the Tapped Out team. How we calculate · All sources.