An ecosystem service approach was used to study the water purification service exemplified by impacts of land management scenarios. Nitrogen retention was calculated in two agricultural catchments by the dynamic Integrated Nutrients in Catchments (INCA)-N model. The monetary valuation was based on purification efficiency of artificial wetlands. The set of scenarios were based on existing agricultural water protection measures, and greening of the Common Agricultural Policy proposal. Scenarios were: wintertime crop cover on fields, increase in area of set aside land, decrease in nitrogen fertilization, crop diversification and nutrient recycling in organic farming. Nitrogen retention provided more value in the Yläneenjoki catchment where the main production line was animal husbandry. In the slowly flowing river Lepsämänjoki, the N retention was more effective than in the fast flowing river Yläneenjoki. When comparing measures some proved to have no value or even a negative value. Set aside had a high positive value when calculated per area, but on a catchment scale the value remained low because of the small area of implementation. Nutrient recycling and winter time vegetation cover were the scenarios that reduced N leaching from fields close to targets set in current political decisions. None of the scenarios increased greenhouse gas emissions.