Water‐soluble pesticides in finished water of community water supplies

To evaluate the effect of the treatment process on pesticide concentration, source water and finished (treated) water samples were collected from 12 community water systems (CWSs) and analyzed for water‐soluble pesticides. The pesticides most frequently detected in the source water were the triazine herbicides (atrazine, cyanazine, prometon, and simazine) and the chloroacetanilide herbicides (acetochlor, alachlor, and metolachlor). Atrazine, metolachlor, prometon, and simazine were detected in the source and finished water of every system sampled. Deethylatrazine, a degradate, was detected in the source and finished water of every CWS but one. The triazine and chloroacetanilide herbicides were usually detected in the finished water after the treatment process, although for most treatment plants the concentrations were significantly less in the finished water. For other pesticides detected in source water—especially the organophosphate insecticides and other sulfur‐containing pesticides (diazinon, chlorpyrifos, malathion, and metribuzin)—the treatment process either removed or degraded the pesticide completely.