In Germany, pesticides can enter tap water in several ways. The main source of contamination is raw water, i.e., groundwater or surface water, before it is treated at the waterworks. Pesticides used on agricultural land (herbicides, insecticides, fungicides) are washed into the soil and then into the groundwater by rain or irrigation. In addition, rain or wind wash pesticides into rivers, lakes, and streams, while industrial or domestic wastewater and contaminated sites can introduce additional residues into the water. 

Raw water plants extract this water from wells or surface waters, which may contain pesticides. Modern water plants use treatment methods to reduce pesticides, such as activated carbon filters (adsorption), ozonation (chemical decomposition), or UV treatment. Precipitation and seasonality, the type of pesticide, and the source of raw water all influence the concentration in tap water: Groundwater is usually less contaminated than surface water, as soil layers retain many substances. 

In Germany, residues ofglyphosate, atrazine, metolachlor, chlortoluron, and several other herbicides are particularly common, but usually in very low concentrations, well below the legal limits. Overall, pesticides enterraw water viaagricultural land, surface water, and seepage processes, and waterworks filter and treat the water in such a way that most residues are greatly reduced. Nevertheless, small traces can enter tap water, especially after heavy rainfall or in regions with intensive agriculture. 

Here explains how the use of certain pesticides (and their degradation products) can contaminate groundwater and drinking water in the long term—despite existing regulations.