# California Water Service - San Mateo, CA — Drinking Water Quality (2026)

> Contaminant levels for the California Water Service - San Mateo, CA public water system from its 2026 Consumer Confidence Report, compared to federal limits.

- Page: https://www.thewatermap.com/water/ca/california-water-service-san-mateo/2026
- JSON API: https://www.thewatermap.com/api/water/ca/california-water-service-san-mateo/2026
- Source: the utility's annual Consumer Confidence Report (CCR)
- Verification: transcribed by a model, cross-checked by a second model, approved before publishing
- Reporting year: 2026
- Contaminants measured: 12
- Contaminants with a federal limit: 2
- Contaminants at or above the federal limit: 0
- Part of The Water Map — https://www.thewatermap.com

## Contaminants measured

| Contaminant | Category | Measured level | Sampling context | Federal limit | Status |
|---|---|---|---|---|---|
| Bromodichloromethane | Disinfection byproducts | 7.128571428571428 UG/L (Average) | Distribution | No federal limit | Detected — no federal limit |
| Bromoform | Disinfection byproducts | 1.0371428571428571 UG/L (Average) | Distribution | No federal limit | Detected — no federal limit |
| Chloroform | Disinfection byproducts | 19.142857142857142 UG/L (Average) | Distribution | No federal limit | Detected — no federal limit |
| Dibromochloromethane | Disinfection byproducts | 3.5285714285714285 UG/L (Average) | Distribution | No federal limit | Detected — no federal limit |
| HAA5 | Disinfection byproducts | 22.125 UG/L (Average) | Distribution | 60 UG/L (MCL) | Within the limit |
| TTHM | Disinfection byproducts | 30.857142857142858 UG/L (Average) | Distribution | 80 UG/L (MCL) | Within the limit |
| Dbaa | Other | 1.2125 UG/L (Average) | Distribution | No federal limit | Detected — no federal limit |
| Dcaa | Other | 13.9125 UG/L (Average) | Distribution | No federal limit | Detected — no federal limit |
| Mbaa | Other | Not detected UG/L (Highest single sample) | Distribution | No federal limit | None detected |
| Mcaa | Other | 1.55 UG/L (Average) | Distribution | No federal limit | Detected — no federal limit |
| Tcaa | Other | 6.225 UG/L (Average) | Distribution | No federal limit | Detected — no federal limit |
| pH | Physical & aggregate | 8.666666666666666 PH (Average) | Distribution | No federal limit | Detected — no federal limit |

## What these contaminants are

- **Bromodichloromethane** — A trihalomethane disinfection byproduct. Counted within regulated total trihalomethanes; long-term exposure is associated with cancer and reproductive effects.
- **Bromoform** — A trihalomethane disinfection byproduct. Counted within regulated total trihalomethanes; long-term exposure is associated with liver and kidney effects.
- **Chloroform** — A trihalomethane formed when chlorine reacts with organic matter in water. A component of regulated total trihalomethanes; long-term exposure is linked to liver and kidney effects.
- **Dibromochloromethane** — A trihalomethane disinfection byproduct. Part of regulated total trihalomethanes; long-term exposure is linked to nervous-system, liver, and kidney effects.
- **HAA5** — Haloacetic acids — a group of five disinfection byproducts formed when disinfectants react with organic matter. Long-term exposure above the federal limit is associated with an increased cancer risk.
- **TTHM** — Total trihalomethanes — a group of four chemicals (including chloroform) formed when chlorine reacts with natural organic matter. Long-term exposure above the federal limit is linked to liver, kidney, and central-nervous-system effects and increased cancer risk.
- **pH** — A measure of how acidic or basic the water is. Regulated only as a secondary standard; very low or high pH can corrode pipes or affect taste.

## How to read this

- A water-quality report covers an entire service area, not a single address.
- 'Federal limit' is the EPA standard (MCL, action level, treatment technique, etc.) that the measured level is compared against.
- 'At or above the federal limit' means the utility's own reported figure met or exceeded that standard.

_Figures are the utility's own published numbers. Generated 2026-05-26 from thewatermap.com._