Portola Improvement Association Mwc, CA
Lead detected, under the action levels
Latest 90th-percentile lead: 0.6 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. 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.
Portola Improvement Association Mwc at a glance
Portola Improvement Association Mwc serves about 80 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: CA4100555; phone on file: 650-947-9687. Ask them for your address in their service line inventory - every system had to publish one by Oct 2024.
Lead results over time
Against the period ending 2025 (0 ppb) the latest result is about the same. The highest 90th-percentile result EPA holds for Portola Improvement Association Mwc is 8.4 ppb across 16 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 0.6 ppb |
| 2025 | 0 (not detected) |
| 2025 | 0 (not detected) |
| 2024 | 0 (not detected) |
| 2024 | 0 (not detected) |
| 2023 | 0.6 ppb |
| 2023 | 0.7 ppb |
| 2022 | 0.7 ppb |
| 2022 | 2 ppb |
| 2021 | 8.4 ppb |
| 2021 | 2.8 ppb |
| 2020 | 1.3 ppb |
| 2020 | 0 (not detected) |
| 2019 | 0 (not detected) |
| 2018 | 0 (not detected) |
| 2016 | 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. Portola Improvement Association Mwc's 0.6 ppb sits at the 66th percentile in California and the 44th nationally (higher means more lead).
Nearby utilities
35 other systems share San Mateo County; 15 of them have a higher latest lead result than Portola Improvement Association Mwc. 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 La Honda, CA
Test your own tap with a certified lab first-draw sample; La Honda, 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 Portola Improvement Association Mwc whether it covers that cost before hiring anyone - many utilities now do. Its latest copper 90th percentile is 1990 ppb (copper action level 1,300 ppb).
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. The lead result guide covers how utilities pick the homes they sample. Systems that went over once often dip back under; here is what that means.