Mendota, IL
Exceeded the action level in the past
Latest 90th-percentile lead: 7.06 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. The latest result is under the action level, but this system has gone over 15 ppb before. Lead comes from pipes, not the source water, so a home with a lead service line can still be exposed. Test your own tap.
Mendota at a glance
Mendota serves about 7,100 people through 2,818 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 groundwater, in Lasalle County, Illinois. EPA system ID: IL0990550; phone on file: 815-539-7459. They can tell you what your service line is made of and whether they pay to replace it.
Every lead result on file
That is down 1.01 ppb from 8.07 ppb in the period ending 2025. The highest 90th-percentile result EPA holds for Mendota is 15.8 ppb across 8 monitoring periods, 1 of them over the 15 ppb action level.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 7.06 ppb |
| 2025 | 8.07 ppb |
| 2025 | 0 (not detected) |
| 2025 | 0 (not detected) |
| 2025 | 15.8 ppb over 15 |
| 2022 | 0 (not detected) |
| 2019 | 7.55 ppb |
| 2016 | 0 (not detected) |
How Mendota 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. Mendota's 7.06 ppb sits at the 93rd percentile in Illinois and the 95th nationally (higher means more lead).
Neighbouring systems
34 other systems share Lasalle County; 3 of them have a higher latest lead result than Mendota. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Il American-Streator | 19,000 | 1 ppb |
| Ottawa | 18,097 | 0 (not detected) |
| Peru | 9,896 | 10.5 ppb |
| La Salle | 9,700 | 0 (not detected) |
| Marseilles | 5,061 | 0 (not detected) |
| Il American-Lake Holiday | 4,750 | 2 ppb |
| Oglesby | 4,500 | 0 (not detected) |
| Seneca | 2,353 | 0 (not detected) |
| Sheridan Correctional Center | 1,670 | 3.6 ppb |
| Earlville | 1,613 | 3.4 ppb |
What to do in your house
Test your own tap with a certified lab first-draw sample; Mendota, 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 Mendota 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. More in what a past exceedance means today.