Drinking water quality, WA
Washington contaminants ranked by SDWA exceedance
Which regulated contaminants exceed their maximum contaminant level (MCL) most often across Washington'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 | - | 5,701 | 0 | 343 |
| 1,1-dichloroethylene | - | 5,701 | 0 | 343 |
| 1,2,4-trichlorobenzene | - | 5,701 | 0 | 343 |
| 1,2-dibromo-3-chloropropane | - | 1,686 | 0 | 240 |
| 1,2-dichloroethane | - | 5,701 | 0 | 343 |
| 1,2-dichloropropane | - | 5,702 | 0 | 343 |
| 2,3,7,8-tcdd | - | 2 | 0 | 2 |
| 2,4,5-tp | - | 3,811 | 0 | 332 |
| 2,4-d | - | 3,811 | 0 | 332 |
| alachlor | - | 2,319 | 0 | 260 |
| antimony, total | inorganic | 4,044 | 0 | 328 |
| arsenic | inorganic | 4,128 | 0 | 329 |
| asbestos | - | 370 | 0 | 172 |
| atrazine | - | 2,331 | 0 | 260 |
| 1,1,1-trichloroethane | - | 5,700 | 0 | 343 |
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.