Drinking water quality, CA
California contaminants ranked by SDWA exceedance
Which regulated contaminants exceed their maximum contaminant level (MCL) most often across California's community water systems, per EPA's Six-Year Review sample-level dataset (2012-2019). Source data is public; every value is citable.
Top 15 contaminants by exceedance count
| Contaminant | Category | Samples | Above MCL | Munis affected |
|---|---|---|---|---|
| 1,1,2-trichloroethane | - | 38,022 | 0 | 973 |
| 1,1-dichloroethylene | - | 43,501 | 0 | 973 |
| 1,2,4-trichlorobenzene | - | 37,896 | 0 | 973 |
| 1,2-dibromo-3-chloropropane | - | 23,613 | 0 | 720 |
| 1,2-dichloroethane | - | 39,916 | 0 | 973 |
| 1,2-dichloropropane | - | 37,998 | 0 | 973 |
| 2,3,7,8-tcdd | - | 4,440 | 0 | 373 |
| 2,4,5-tp | - | 8,716 | 0 | 597 |
| 2,4-d | - | 9,221 | 0 | 636 |
| alachlor | - | 13,674 | 0 | 708 |
| antimony, total | inorganic | 23,632 | 0 | 983 |
| arsenic | inorganic | 74,228 | 0 | 988 |
| asbestos | - | 4,532 | 0 | 640 |
| atrazine | - | 15,181 | 0 | 753 |
| 1,1,1-trichloroethane | - | 39,071 | 0 | 973 |
For citizens
Look up your own water system by name on the muni search, then read the drinking-water quality band on its profile page for per-contaminant readings + MCL ratios.
For chemical suppliers
Contaminants near or above MCL signal treatment-chemical procurement pressure. Lane intelligence pairs this with per-chemical bid timing on the supplier tier.