Compliance record
Formal violations the EPA has on file for this supplier. A health-based violation means a contaminant limit or a required treatment was breached; the rest are monitoring or reporting failures — still violations, but not a measured health risk.
| Violation | Type | Status | Period |
|---|---|---|---|
| TT | Health-based | Resolved | 1993-06-01 → 1993-06-30 |
| TT | Health-based | Resolved | 1993-06-01 → 1993-06-30 |
| MCL | Health-based | Resolved | 1992-10-01 → 1992-10-31 |
Other contaminants detected
| Contaminant | Level vs EPA limit | Detection rate | Source | Period |
|---|---|---|---|---|
| Dichloroacetic Acid | 31 µg/L No EPA limit set
worst single sample: 39 µg/L | 257/257 | SYR4 | 2012–2019 |
| Total Haloacetic Acids (HAA5) | 54.2 µg/L 90% of the EPA limit 60 µg/L
worst single sample: 67 µg/L | 257/257 | SYR4 | 2012–2019 |
| Trichloroacetic Acid | 25 µg/L No EPA limit set
worst single sample: 30 µg/L | 256/257 | SYR4 | 2012–2019 |
| Chloroform | 51.043 µg/L No EPA limit set
worst single sample: 73.4 µg/L | 255/256 | SYR4 | 2012–2019 |
| TTHM | 53 µg/L 66% of the EPA limit 80 µg/L
worst single sample: 85.3 µg/L | 255/256 | SYR4 | 2012–2019 |
| Bromodichloromethane | 7.486 µg/L No EPA limit set
worst single sample: 10.97 µg/L | 238/256 | SYR4 | 2012–2019 |
| Dibromochloromethane | 3.54 µg/L No EPA limit set
worst single sample: 6.02 µg/L | 76/256 | SYR4 | 2012–2019 |
| Monochloroacetic Acid | 3 µg/L No EPA limit set
worst single sample: 3.5 µg/L | 53/257 | SYR4 | 2012–2019 |
| Lead | 0.0044 mg/L 29% of the EPA limit 0.0150 mg/L | 42/42 | LCR | 2025 |
| Bromoform | 3.406 µg/L No EPA limit set
worst single sample: 3.47 µg/L | 17/256 | SYR4 | 2012–2019 |
| Dibromoacetic Acid | 2.12 µg/L No EPA limit set
worst single sample: 2.2 µg/L | 9/257 | SYR4 | 2012–2019 |
| Copper | 228.32 µg/L 18% of the EPA limit 1300 µg/L
worst single sample: 233.408 µg/L | 6/7 | SYR4 | 2016–2019 |
| Monobromoacetic Acid | 1.1 µg/L No EPA limit set | 2/257 | SYR4 | 2012–2019 |
| Lead | 14.656 µg/L 98% of the EPA limit 15 µg/L | 1/7 | SYR4 | 2016–2019 |
30 contaminants tested, none detected
Utility contact
Frequently asked questions about California Water Service - San Mateo
Is California Water Service - San Mateo tap water safe to drink?
EPA monitoring detected 14 contaminants in California Water Service - San Mateo's water. A detection isn't the same as a violation — most levels are within federal limits. See each level and source above, and the utility's annual Consumer Confidence Report for its official compliance status.
What contaminants were detected in California Water Service - San Mateo's water?
EPA monitoring detected Dichloroacetic Acid, Total Haloacetic Acids (HAA5), Trichloroacetic Acid, Chloroform, TTHM, and others. The full list with the level and data source for each is above.
How many people does California Water Service - San Mateo serve?
California Water Service - San Mateo reports serving 102,348 people in California, per its EPA record.
Has California Water Service - San Mateo had any water quality violations?
The EPA has 3 violations on file for California Water Service - San Mateo, of which 3 are health-based (a contaminant limit or required treatment was breached) and 0 remain open. The rest are monitoring or reporting failures.
Where does this data come from?
Every figure is official EPA drinking-water monitoring — the Lead & Copper Rule, the UCMR-5 nationwide testing program, and the EPA Six-Year Review — not our own testing. Each number is labelled with its source and period.