Coastside County Water District, CA
Lead detected, under the action levels
Latest 90th-percentile lead: 1.6 ppb (monitoring period 2022-2024). 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.
About Coastside County Water District
Coastside County Water District serves about 19,033 people through 6,634 service connections, which makes it a large 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: CA4110011; phone on file: 650-276-0889. Ask them for your address in their service line inventory - every system had to publish one by Oct 2024.
Every lead result on file
That is down 1.1 ppb from 2.7 ppb in the period ending 2021. The highest 90th-percentile result EPA holds for Coastside County Water District is 7 ppb across 4 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2024 | 1.6 ppb |
| 2021 | 2.7 ppb |
| 2018 | 0 (not detected) |
| 2016 | 7 ppb |
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. Coastside County Water District's 1.6 ppb sits at the 76th percentile in California and the 65th nationally (higher means more lead).
Neighbouring systems
35 other systems share San Mateo County; 14 of them have a higher latest lead result than Coastside County Water District. 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 Half Moon Bay, CA
Test your own tap with a certified lab first-draw sample; Half Moon Bay, 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 Coastside County Water District 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. Why sampled homes are the worst-case ones is in the guide to reading the number. The action level is dropping - the 10 ppb rule from 2027.