This article investigates from the perspectives of water protection and economy whether arable cropping is adapted to site conditions in the catchment of Lake Greifensee. Field studies demonstrate that herbicide losses to surface waters can vary strongly for different areas. Large losses can be expected from poorly drained fields with a direct hydrological connection to the stream. To identify such risk areas an indicator was developed, which allows for a linkage with the land use expected from economical reasoning. The indicator is strongly correlated with the site specific suitability for different agronomic land use. This suitability largely controls the outcome of the economically predicted optimal land use. In reality, land use deviates substantially from the theoretical optimum. As a consequence, cereals and corn are produced on risk areas to the same extend as other crops including grassland. Model calculations show that the existing land use could be obtained in a more site adapted manner without restrictions due to property rights. As a consequence, less arable crops would cover risk areas.