Oak Brook, IL
Lead detected, under the action levels
Latest 90th-percentile lead: 0.49 ppb (monitoring period 2024-2026). 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.
Who runs the water here
Oak Brook serves about 9,400 people through 3,295 service connections, which makes it a medium-sized 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: IL0430700; phone on file: 630-368-5276. Call that number and ask whether your address has a lead, galvanized or unknown service line.
Every lead result on file
Against the period ending 2025 (0.83 ppb) the latest result is about the same. The highest 90th-percentile result EPA holds for Oak Brook is 2.86 ppb across 5 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 0.49 ppb |
| 2025 | 0.83 ppb |
| 2023 | 2.11 ppb |
| 2020 | 0 (not detected) |
| 2017 | 2.86 ppb |
Against other Illinois systems
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. Oak Brook's 0.49 ppb sits at the 55th percentile in Illinois and the 43rd nationally (higher means more lead).
Neighbouring systems
47 other systems share Dupage County; 25 of them have a higher latest lead result than Oak Brook. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Naperville | 156,406 | 6.1 ppb |
| 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 |
Your move
Test your own tap with a certified lab first-draw sample; Oak Brook, 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 Oak Brook 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. What a 90th-percentile result does and does not tell you: how to read a lead result. Size matters more than most people expect: small vs large water systems.