Yosemite West Water System, CA
Lead detected, under the action levels
Latest 90th-percentile lead: 2.2 ppb (monitoring period 2020-2022). 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.
Yosemite West Water System at a glance
Yosemite West Water System serves about 420 people through 185 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 groundwater, in Mariposa County, California. EPA system ID: CA2210924; phone on file: 209-966-5356. Call that number and ask whether your address has a lead, galvanized or unknown service line.
Yosemite West Water System's lead record
That is down 3.6 ppb from 5.8 ppb in the period ending 2019. The highest 90th-percentile result EPA holds for Yosemite West Water System is 5.8 ppb across 3 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2022 | 2.2 ppb |
| 2019 | 5.8 ppb |
| 2016 | 3.6 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. Yosemite West Water System's 2.2 ppb sits at the 80th percentile in California and the 75th nationally (higher means more lead).
Nearby utilities
10 other systems share Mariposa County; 3 of them have a higher latest lead result than Yosemite West Water System. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Mariposa Public Utility Dist | 2,000 | 0 (not detected) |
| Yosemite Nps-Yosemite Valley | 1,000 | 0 (not detected) |
| Ponderosa Basin Mutual Wtr Co | 798 | 0 (not detected) |
| Yosemite Nps-El Portal | 635 | 0 (not detected) |
| Mariposa Pines Mutual | 294 | 0 (not detected) |
| Mpwd-Coulterville Csa 1 | 193 | 1.4 ppb |
| Yosemite Nps-Wawona | 150 | 0 (not detected) |
| Yosemite Terrace Estates | 130 | 6.6 ppb |
| Mcclure Boat Club, Inc. | 36 | 10 ppb |
| Cedar Lodge | 28 | 3.7 ppb |
What to do in your house
Test your own tap with a certified lab first-draw sample; Mariposa, 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 Yosemite West Water System 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. The action level is dropping - the 10 ppb rule from 2027.