Loma Mar Mutual, CA
Lead detected, under the action levels
Latest 90th-percentile lead: 2.8 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
Loma Mar Mutual serves about 65 people through 34 service connections, which makes it a very small system under EPA's size classes. It is privately owned and draws surface water, in San Mateo County, California. EPA system ID: CA4100512; phone on file: 650-879-9638. They can tell you what your service line is made of and whether they pay to replace it.
Lead results over time
That is up 2.8 ppb from 0 ppb in the period ending 2025. The highest 90th-percentile result EPA holds for Loma Mar Mutual is 3 ppb across 5 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 2.8 ppb |
| 2025 | 0 (not detected) |
| 2022 | 0 (not detected) |
| 2019 | 0 (not detected) |
| 2016 | 3 ppb |
Where this result ranks
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. Loma Mar Mutual's 2.8 ppb sits at the 83rd percentile in California and the 79th nationally (higher means more lead).
Neighbouring systems
35 other systems share San Mateo County; 10 of them have a higher latest lead result than Loma Mar Mutual. 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 Loma Mar, CA
Test your own tap with a certified lab first-draw sample; Loma Mar, 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 Loma Mar Mutual 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.