# Coastside County Water District — Half Moon Bay, Ca, CA — Drinking Water Quality (2023)

> Contaminant levels for the Coastside County Water District — Half Moon Bay, Ca, CA public water system from its 2023 Consumer Confidence Report, compared to federal limits.

- Page: https://www.thewatermap.com/water/ca/coastside-county-water-district-half-moon-bay-ca/2023
- JSON API: https://www.thewatermap.com/api/water/ca/coastside-county-water-district-half-moon-bay-ca/2023
- 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: 2023
- Contaminants measured: 11
- Contaminants with a federal limit: 4
- 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 |
|---|---|---|---|---|---|
| Chlorine | Disinfectants | 0.84 mg/L (Average) | System-wide | No federal limit | Within the limit |
| HAA5 | Disinfection byproducts | 27 ug/L (Running annual avg) | Location RAA | No federal limit | Within the limit |
| TTHM | Disinfection byproducts | 60 ug/L (Running annual avg) | Location RAA | No federal limit | Within the limit |
| Fluoride | Inorganic chemicals | 0.2 mg/L (Average) | Denniston WTP | 4 mg/L (MCL) | Within the limit |
| Nitrate | Inorganic chemicals | 0.4 mg/L (Average) | Nunes WTP | 10 mg/L (MCL) | Within the limit |
| Aluminum | Metals | Not detected mg/L (Average) | Nunes WTP | No federal limit | Detected — no federal limit |
| Boron | Metals | Not detected ug/L (Range) | Denniston WTP | 1000 ug/L (NL) | None detected |
| Copper | Metals | 0.08 mg/L (90th percentile) | At the tap | 1.3 mg/L (Action level) | Within the limit |
| Lead | Metals | 1.7 ug/L (90th percentile) | At the tap | No federal limit | Within the limit |
| TOC | Physical & aggregate | 1.2 mg/L (Average) | Denniston WTP | No federal limit | Detected — no federal limit |
| Turbidity | Physical & aggregate | 0.025 NTU (Average) | Nunes WTP | No federal limit | Within the limit |

## What these contaminants are

- **Chlorine** — A disinfectant added to drinking water to kill bacteria and viruses. Effective and necessary, but high residual levels can cause taste and odor issues; the EPA caps the residual disinfectant level.
- **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.
- **Fluoride** — A mineral often added to drinking water to help prevent tooth decay. Beneficial at low levels, but long-term exposure above the federal limit can cause bone disease and tooth mottling.
- **Nitrate** — A compound from fertilizer runoff, septic systems, and erosion of natural deposits. Levels above the federal limit can cause 'blue baby syndrome,' a serious oxygen-transport condition in infants.
- **Aluminum** — A common element sometimes used as a treatment coagulant. Regulated only as a secondary (cosmetic) standard; high levels can discolor water.
- **Boron** — A naturally occurring element from rock and soil. No enforceable federal limit; the EPA has issued a health advisory level.
- **Copper** — A metal that enters water from corroding household plumbing. Short-term exposure causes stomach distress; long-term exposure can damage the liver and kidneys.
- **Lead** — A toxic metal that leaches into water from old service lines, solder, and plumbing fixtures. There is no safe level of lead; it harms brain development in children and raises blood pressure in adults. The EPA sets an action level, not a health goal above zero.
- **TOC** — Total organic carbon — a measure of organic material dissolved in the water. Not harmful itself, but it is the raw material that forms disinfection byproducts; removal is a treatment requirement.
- **Turbidity** — A measure of cloudiness from suspended particles in the water. High turbidity can shelter microbes from disinfection; the EPA enforces it through a treatment-technique standard.

## 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 2026-06-04 from thewatermap.com._