Naperville, IL
Lead detected, under the action levels
Latest 90th-percentile lead: 6.1 ppb (monitoring period 2026-2026). The federal action level is 15 ppb today and drops to 10 ppb in Nov 2027; EPA's health goal is 0. Lead was measured in sampled homes but the 90th percentile is under both action levels. EPA's health goal for lead is zero, so test your own tap if your home was built before 1986 or anyone in it is pregnant or a young child.
Naperville at a glance
Naperville serves about 156,406 people through 45,580 service connections, which makes it a very large system under EPA's size classes. It is owned by a local government (city, town, county or district) and draws surface water, in Dupage County, Illinois. EPA system ID: IL0434670; phone on file: 630-420-6125. Call that number and ask whether your address has a lead, galvanized or unknown service line.
Lead results over time
That is up 6.1 ppb from 0 ppb in the period ending 2025. The highest 90th-percentile result EPA holds for Naperville is 7.1 ppb across 10 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 6.1 ppb |
| 2025 | 0 (not detected) |
| 2025 | 0 (not detected) |
| 2025 | 7.1 ppb |
| 2025 | 4.7 ppb |
| 2024 | 4.2 ppb |
| 2023 | 5.06 ppb |
| 2022 | 0 (not detected) |
| 2021 | 5.14 ppb |
| 2018 | 0 (not detected) |
How Naperville compares
Of the 1,744 Illinois systems with a lead result, the median latest reading is 0 ppb; 22 are over 15 ppb right now and 152 have gone over at some point. Naperville's 6.1 ppb sits at the 90th percentile in Illinois and the 94th nationally (higher means more lead).
Other water systems in Dupage County
47 other systems share Dupage County; 5 of them have a higher latest lead result than Naperville. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Wheaton | 53,970 | 2.32 ppb |
| Downers Grove | 49,425 | 4.98 ppb |
| Elmhurst | 45,000 | 5.52 ppb |
| Lombard | 44,476 | 10.6 ppb |
| Carol Stream | 39,854 | 1.05 ppb |
| Addison | 38,017 | 2 ppb |
| Woodridge | 33,566 | 0 (not detected) |
| Glendale Heights | 33,176 | 0 (not detected) |
| Glen Ellyn | 28,500 | 1.87 ppb |
| West Chicago | 25,166 | 0.52 ppb |
What to do in your house
Test your own tap with a certified lab first-draw sample; Naperville, IL may offer free or low-cost kits through the utility. If your own line is lead, replacing the private side runs about $1,200-$12,300 (EPA average about $4,700). Ask Naperville whether it covers that cost before hiring anyone - many utilities now do.
These figures describe homes the utility sampled, not your tap. Only your service line record or a test of your own water answers the question for your house. The lead result guide covers how utilities pick the homes they sample. Systems that went over once often dip back under; here is what that means.