Metolachlor is an herbicide used on crops that can enter drinking water through agricultural runoff. It may contaminate both groundwater and surface water sources.

Metolachlor, introduced in 1976, is a widely used herbicide for controlling grasses and broadleaf weeds in crops like corn and soybeans. It can enter water supplies through agricultural runoff and soil leaching. Water utilities measure metolachlor levels in parts per billion (ppb). While moderately persistent in the environment, it can potentially contaminate both surface and groundwater sources. The EPA has set a lifetime health advisory level for metolachlor in drinking water, though more research is needed on its long-term health effects.