What was found in San Dimas's water
The level at the city's main supplier, the highest level anywhere in the city, the EPA limit for each, and where every figure comes from.
| Contaminant | Level vs EPA limit | Suppliers | Source |
|---|---|---|---|
| Nitrate | 4885.7 µg/L 49% of the EPA limit 10000 µg/L Highest in the city: GSWC-SOUTH ARCADIA · 27,072 people · 2019 | 1/4 | SYR4 |
| Nitrate-Nitrite | 4610 µg/L 46% of the EPA limit 10000 µg/L Highest in the city: GSWC-SOUTH ARCADIA · 27,072 people · 2019 | 1/4 | SYR4 |
| Fluoride | 853 µg/L 21% of the EPA limit 4000 µg/L Highest in the city: GSWC-SOUTH ARCADIA · 27,072 people · 2019 | 1/4 | SYR4 |
| Copper | 190 µg/L 15% of the EPA limit 1300 µg/L Highest in the city: GSWC-SOUTH SAN GABRIEL · 26,240 people · 2019 | 1/4 | SYR4 |
| TTHM | 59.65 µg/L 75% of the EPA limit 80 µg/L Main supplier: GSWC-SAN DIMAS · 56,538 people · 2019 | 4/4 | SYR4 |
| Lithium | 57 µg/L No EPA limit set Main supplier: GSWC-SAN DIMAS · 56,538 people · 2025 | 2/4 | UCMR-5 |
| Total Haloacetic Acids (HAA5) | 23 µg/L 38% of the EPA limit 60 µg/L Main supplier: GSWC-SAN DIMAS · 56,538 people · 2019
Highest in the city: 24.8 µg/L — GSWC - CLAREMONT · 39,730 people · 2019 | 4/4 | SYR4 |
| Chloroform | 23 µg/L No EPA limit set Main supplier: GSWC-SAN DIMAS · 56,538 people · 2019 | 4/4 | SYR4 |
| Dibromochloromethane | 22 µg/L No EPA limit set Main supplier: GSWC-SAN DIMAS · 56,538 people · 2019 | 4/4 | SYR4 |
| Bromodichloromethane | 20 µg/L No EPA limit set Main supplier: GSWC-SAN DIMAS · 56,538 people · 2019 | 4/4 | SYR4 |
| Lead | 17 µg/L 113% of the EPA limit, at the 95th percentile of samples — 15 µg/L Highest in the city: GSWC-SOUTH SAN GABRIEL · 26,240 people · 2019 | 1/4 | SYR4 |
| Trichloroethylene | 14 µg/L 280% of the EPA limit, at the 95th percentile of samples — 5 µg/L Highest in the city: GSWC-SOUTH ARCADIA · 27,072 people · 2019 | 1/4 | SYR4 |
| Bromoform | 12 µg/L No EPA limit set Main supplier: GSWC-SAN DIMAS · 56,538 people · 2019 | 4/4 | SYR4 |
| Dichloroacetic Acid | 12 µg/L No EPA limit set Main supplier: GSWC-SAN DIMAS · 56,538 people · 2019 | 3/4 | SYR4 |
| Trichloroacetic Acid | 8.845 µg/L No EPA limit set Main supplier: GSWC-SAN DIMAS · 56,538 people · 2019 | 3/4 | SYR4 |
| Dibromoacetic Acid | 7.405 µg/L No EPA limit set Main supplier: GSWC-SAN DIMAS · 56,538 people · 2019
Highest in the city: 7.8 µg/L — GSWC - CLAREMONT · 39,730 people · 2019 | 4/4 | SYR4 |
| Tetrachloroethylene | 6.04 µg/L 121% of the EPA limit, at the 95th percentile of samples — 5 µg/L Highest in the city: GSWC-SOUTH ARCADIA · 27,072 people · 2019 | 1/4 | SYR4 |
| Monochloroacetic Acid | 4.875 µg/L No EPA limit set Highest in the city: GSWC - CLAREMONT · 39,730 people · 2019 | 3/4 | SYR4 |
| Combined Uranium | 4.3061 µg/L 14% of the EPA limit 30 µg/L Highest in the city: GSWC-SOUTH ARCADIA · 27,072 people · 2018 | 1/4 | SYR4 |
| Monobromoacetic Acid | 4.265 µg/L No EPA limit set Highest in the city: GSWC - CLAREMONT · 39,730 people · 2019 | 1/4 | SYR4 |
| Dichloromethane | 3.32 µg/L 66% of the EPA limit 5 µg/L Highest in the city: GSWC-SOUTH ARCADIA · 27,072 people · 2019 | 1/4 | SYR4 |
| PFOS | 0.0045 µg/L No EPA limit set Main supplier: GSWC-SAN DIMAS · 56,538 people · 2025
Highest in the city: 0.0220 µg/L — GSWC-SOUTH ARCADIA · 27,072 people · 2024 | 3/4 | UCMR-5 |
| PFOA | 0.0129 µg/L No EPA limit set Highest in the city: GSWC - CLAREMONT · 39,730 people · 2024 | 2/4 | UCMR-5 |
| Pfhxa | 0.0084 µg/L No EPA limit set Highest in the city: GSWC - CLAREMONT · 39,730 people · 2024 | 1/4 | UCMR-5 |
| PFHXS | 0.0070 µg/L No EPA limit set Highest in the city: GSWC-SOUTH ARCADIA · 27,072 people · 2024 | 2/4 | UCMR-5 |
| Pfpea | 0.0064 µg/L No EPA limit set Highest in the city: GSWC - CLAREMONT · 39,730 people · 2024 | 1/4 | UCMR-5 |
| Lead | 0.0021 mg/L 14% of the EPA limit 0.0150 mg/L Main supplier: GSWC-SAN DIMAS · 56,538 people · 2026
Highest in the city: 0.0056 mg/L — GSWC - CLAREMONT · 39,730 people · 2026 | 4/4 | LCR |
| Pfba | 0.0056 µg/L No EPA limit set Highest in the city: GSWC-SOUTH SAN GABRIEL · 26,240 people · 2024 | 1/4 | UCMR-5 |
| PFBS | 0.0051 µg/L No EPA limit set Highest in the city: GSWC - CLAREMONT · 39,730 people · 2024 | 1/4 | UCMR-5 |
| Pfhpa | 0.0046 µg/L No EPA limit set Highest in the city: GSWC - CLAREMONT · 39,730 people · 2024 | 1/4 | UCMR-5 |
Each bar shows the measured level as a share of the EPA limit: green is
well under, amber is close to it, red is over. For lead and copper the
limit applies to exactly the 90th-percentile figure shown, so red there
means a real exceedance. For everything else the limit applies to a
running annual average while the figure is the 95th percentile of the
system's samples — over 100% is worth reading, but is not by itself a
violation.
Formal violations are listed separately.
These are the utilities' own EPA-reported results, not a city-wide
average. A detection means the lab measured the
substance — it isn't the same as exceeding a legal limit. Hover a source
tag to see the EPA program and years behind each figure.
Water suppliers serving San Dimas
| Supplier | Population served |
|---|---|
| GSWC-SAN DIMAS | 56,538 |
| GSWC - CLAREMONT | 39,730 |
| GSWC-SOUTH ARCADIA | 27,072 |
| GSWC-SOUTH SAN GABRIEL | 26,240 |
Frequently asked questions about San Dimas tap water
Is San Dimas tap water safe to drink?
EPA testing detected 30 contaminants in the water serving San Dimas. A detection isn't the same as a violation — most detected levels are within federal limits. Check the level and source for each contaminant above, and your utility's annual Consumer Confidence Report for the official compliance status.
How many water suppliers serve San Dimas?
4 public water suppliers report drinking-water monitoring for San Dimas, California to the EPA. Each is listed above with its population served.
What contaminants are in San Dimas's water?
The contaminants EPA monitoring detected in San Dimas include Nitrate, Nitrate-Nitrite, Fluoride, Copper, TTHM. The full list, with the level at the main supplier and the data source, is in the table above.
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.