Castlewood Domestic Water System, CA
Exceeded the action level in the past
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 result is under the action level, but this system has gone over 15 ppb before. Lead comes from pipes, not the source water, so a home with a lead service line can still be exposed. Test your own tap.
Castlewood Domestic Water System at a glance
Castlewood Domestic Water System serves about 524 people through 207 service connections, which makes it a small system under EPA's size classes. It is owned by a local government (city, town, county or district) and draws groundwater, in Alameda County, California. EPA system ID: CA0105008; phone on file: 510-670-5241. They can tell you what your service line is made of and whether they pay to replace it.
Castlewood Domestic Water System's lead record
That is down 41 ppb from 41 ppb in the period ending 2023. The highest 90th-percentile result EPA holds for Castlewood Domestic Water System is 41 ppb across 4 monitoring periods, 2 of them over the 15 ppb action level.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 0 (not detected) |
| 2023 | 41 ppb over 15 |
| 2020 | 24.5 ppb over 15 |
| 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. Castlewood Domestic Water System's reported as 0 (not detected) sits at the 37th percentile in California and the 23rd nationally (higher means more lead). Systems reporting 0 tie at the bottom, so the rank mostly reflects size among them.
Nearby utilities
13 other systems share Alameda County; 3 of them have a higher latest lead result than Castlewood Domestic Water System. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| East Bay Mud | 1,468,000 | 0 (not detected) |
| Alameda County Water District | 344,000 | 0 (not detected) |
| City Of Hayward | 162,954 | 0 (not detected) |
| Dublin San Ramon Services District | 98,776 | 0 (not detected) |
| City Of Pleasanton | 76,689 | 0 (not detected) |
| California Water Service - Livermore | 60,414 | 7.5 ppb |
| City Of Livermore | 38,892 | 0 (not detected) |
| Alameda Point | 600 | 0 (not detected) |
| Trailer Haven Mobile Home Park | 459 | 2.7 ppb |
| Town Of Sunol - Sfpuc | 281 | 0 (not detected) |
Your move
Test your own tap with a certified lab first-draw sample; Pleasanton, 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 Castlewood Domestic 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. Why an old exceedance still matters: over the limit before, under it now.