Tud - Upper Basin Water System, CA
Lead reported as not detected
Latest 90th-percentile lead: reported as 0 (not detected) (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. The latest 90th-percentile result was reported as 0 (not detected at the lab's limit). That says the sampled homes were low, not that your home has no lead service line. Check your utility's service line inventory for your address.
Who runs the water here
Tud - Upper Basin Water System serves about 13,331 people through 4,907 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 Tuolumne County, California. EPA system ID: CA5510012; phone on file: 209-532-5536. They can tell you what your service line is made of and whether they pay to replace it.
Every lead result on file
Against the period ending 2023 (0 ppb) the latest result is about the same. The highest 90th-percentile result EPA holds for Tud - Upper Basin Water System is 0 ppb across 4 monitoring periods, none of them over 15 ppb.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 0 (not detected) |
| 2023 | 0 (not detected) |
| 2020 | 0 (not detected) |
| 2017 | 0 (not detected) |
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. Tud - Upper Basin Water System's reported as 0 (not detected) sits at the 54th percentile in California and the 38th nationally (higher means more lead). Systems reporting 0 tie at the bottom, so the rank mostly reflects size among them.
Nearby utilities
48 other systems share Tuolumne County; 16 of them have a higher latest lead result than Tud - Upper Basin Water System. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| Tud - Sonora/Jamestown Water System | 11,113 | 0 (not detected) |
| Tud - Columbia Water System | 5,482 | 5.4 ppb |
| Cdcr - Sierra Conservation Center | 3,571 | 0 (not detected) |
| Groveland Community Serv Dist | 3,400 | 0 (not detected) |
| Twain Harte Community Services District | 2,378 | 0 (not detected) |
| Tud - Tuolumne Water System | 1,798 | 0 (not detected) |
| Tud - Ponderosa | 1,781 | 0 (not detected) |
| Cold Springs Water Co | 1,771 | 2.8 ppb |
| Lake Don Pedro Csd | 1,700 | 0 (not detected) |
| Phoenix Lake Estates Cc Mwc | 1,168 | 0 (not detected) |
Next steps for Sonora, CA
Look up your address in Tud - Upper Basin Water System's service line inventory. If it says lead, galvanized or unknown, test your tap. If your own line is lead, replacing the private side runs about $1,200-$12,300 (EPA average about $4,700). Ask Tud - Upper Basin 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. Why sampled homes are the worst-case ones is in the guide to reading the number. A zero today does not rule out a jump later - the rules are tightening in 2027.