The metabolism of nitrate was investigated on a Northern German Aquifer within the catchment area of a water works. The reaction kinetic of nitrate decay was determined with help of laboratory and field investigations. Thus the metabolisms potential as well as the relevant reactive material is distributed heterogeneous within the aquifer. This is considered by a numeric transport model. By means of this model the impact of land use changes on nitrate concentration of ground- and raw water was calculated. The model shows that the change of arable land into forestal and extensive grassland use will not affect raw water quality during the next 15 years.