We studied trifluoroacetate (TFA) in a German river catchment. TFA from rain was not permanently retained in soils or plants and can be mobilized  by heavy rain, meaning soils and plants may hold more TFA than rivers or rainfall indicate. In areas with precipitation input only, TFA served as a new tracer for determining actual evapotranspiration. The agricultural area showed higher TFA in surface and groundwater, suggesting that agriculture increases TFA pollution.