Life cycle assessments (LCA) calculate the environmental impact of products by evaluating all fluxes of energy and materials throughout the entire life cycle of the product, from resource extraction to waste disposal. Until recently, the majority of LCAs was restricted to the industrial part of the production chain notwithstanding the potential environmental impact of biological production. This incited an ongoing revision of the existing methodology for incorporation of the impacts of agricultural or forestry practices. The overall aim of this research is to extend the available LCA methodology to cover the impacts of land use on the water balance. In a first phase, an adequate impact description will be developed based on the available literature and methodological reasoning. This means that indicator variables have to be identified that describe all potential water related impacts of land use systems. Thereafter, in the impact calculation indicator scores are quantified for specific land use scenarios from more generally available data making use of the catchment scale hydrological model SWAT. Special attention is paid to the problem of model parameter estimation in ungauged catchments. The last phase involves the impact evaluation that calculates the uncertainty on the results of the impact analysis.