County Service Area 7, CA
Exceeded the action level in the past
Latest 90th-percentile lead: 1.8 ppb (monitoring period 2026-2028). 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.
About County Service Area 7
County Service Area 7 serves about 300 people through 69 service connections, which makes it a very small system under EPA's size classes. It is owned by a local government (city, town, county or district) and draws surface water, in San Mateo County, California. EPA system ID: CA4100509; phone on file: 650-599-7390. They can tell you what your service line is made of and whether they pay to replace it.
Lead results over time
Against the period ending 2025 (2.1 ppb) the latest result is about the same. The highest 90th-percentile result EPA holds for County Service Area 7 is 46 ppb across 15 monitoring periods, 1 of them over the 15 ppb action level.
| Period ending | 90th-percentile lead |
|---|---|
| 2028 | 1.8 ppb |
| 2025 | 2.1 ppb |
| 2025 | 1.8 ppb |
| 2024 | 1.7 ppb |
| 2024 | 1.1 ppb |
| 2023 | 2.8 ppb |
| 2023 | 2.4 ppb |
| 2022 | 3.3 ppb |
| 2022 | 3.5 ppb |
| 2021 | 1.9 ppb |
| 2021 | 4.1 ppb |
| 2020 | 5.8 ppb |
| 2020 | 0 (not detected) |
| 2018 | 46 ppb over 15 |
| 2017 | 0 (not detected) |
Against other California systems
Of the 2,884 California systems with a lead result, the median latest reading is 0 ppb; 30 are over 15 ppb right now and 215 have gone over at some point. County Service Area 7's 1.8 ppb sits at the 77th percentile in California and the 67th nationally (higher means more lead).
Other water systems in San Mateo County
35 other systems share San Mateo County; 13 of them have a higher latest lead result than County Service Area 7. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| California Water Service - San Mateo | 103,536 | 4.4 ppb |
| City Of Daly City | 102,593 | 0 (not detected) |
| City Of Redwood City | 90,043 | 0 (not detected) |
| California Water Service-S San Francisco | 62,609 | 4.1 ppb |
| California Water Service - Bear Gulch | 60,382 | 4 ppb |
| City Of San Bruno | 42,631 | 0 (not detected) |
| North Coast County Water Dist | 38,546 | 0 (not detected) |
| Estero Municipal Improvement District | 36,556 | 0 (not detected) |
| California Water Service - San Carlos | 34,801 | 5.8 ppb |
| City Of Burlingame | 32,453 | 6.3 ppb |
Next steps for Redwood City, CA
Test your own tap with a certified lab first-draw sample; Redwood City, CA 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 County Service Area 7 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. Why an old exceedance still matters: over the limit before, under it now.