Gran Cielo Mutual Water Company, CA
Above the federal action level
Latest 90th-percentile lead: 21 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. In the most recent monitoring period, more than 10% of the sampled homes measured above 15 ppb. Use a filter certified to NSF/ANSI 53 for lead for drinking and cooking now, and test your own tap.
Who runs the water here
Gran Cielo Mutual Water Company serves about 139 people through 42 service connections, which makes it a very small system under EPA's size classes. It is privately owned and draws groundwater, in San Luis Obispo County, California. EPA system ID: CA4000853; phone on file: 805-459-8498. Ask them for your address in their service line inventory - every system had to publish one by Oct 2024.
Gran Cielo Mutual Water Company's lead record
The highest 90th-percentile result EPA holds for Gran Cielo Mutual Water Company is 21 ppb across 1 monitoring period, 1 of them over the 15 ppb action level.
| Period ending | 90th-percentile lead |
|---|---|
| 2026 | 21 ppb over 15 |
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. Gran Cielo Mutual Water Company's 21 ppb sits at the 99th percentile in California and the 99th nationally (higher means more lead).
Nearby utilities
71 other systems share San Luis Obispo County; 1 of them has a higher latest lead result than Gran Cielo Mutual Water Company. If you are unsure which one supplies your house, the name on your water bill decides it.
| System | People | Latest lead |
|---|---|---|
| San Luis Obispo Water Department | 49,534 | 0 (not detected) |
| Atascadero Mutual Water Co | 33,307 | 0 (not detected) |
| City Of Paso Robles Water Division | 31,176 | 0 (not detected) |
| City Of Arroyo Grande Utilities Division | 17,963 | 0 (not detected) |
| California Mens Colony | 15,000 | 0 (not detected) |
| Nipomo Comm Services Dist | 13,771 | 0 (not detected) |
| City Of Grover Beach Public Works Dept | 12,701 | 0 (not detected) |
| Morro Bay Pw Dept - Water Division | 10,757 | 0 (not detected) |
| Templeton Csd | 8,041 | 0 (not detected) |
| Pismo Beach Water Department | 7,944 | 0 (not detected) |
Next steps for Los Osos, CA
Use a filter certified to NSF/ANSI 53 for lead on the tap you drink and cook from, now, before you test. Then test your own tap. If your own line is lead, replacing the private side runs about $1,200-$12,300 (EPA average about $4,700). Ask Gran Cielo Mutual Water Company 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.