Chlorpyrifos is a pesticide used on crops that can enter drinking water through agricultural runoff. It harms brain development in children and was banned for home use.

Chlorpyrifos is an organophosphate insecticide widely used in agriculture since the 1960s. It can contaminate water sources through agricultural runoff and soil erosion. The EPA banned its residential use in 2001 and all food uses in 2021 due to health concerns, particularly its potential impact on children's brain development. Water utilities typically measure chlorpyrifos levels in parts per billion (ppb). While its use has decreased, it may still be present in some water sources due to its persistence in the environment.