The European Treaty supports the application of the polluter pays principle in all environmental policies including the Water Framework Directive. This paper assesses the efficiency of water-charging systems in two European regions. The regions examined are the South west region of Ireland and the Navarre region in Spain which were selected because they are similar in terms of economic indicators but different in terms of water pricing structures. The paper describes the development and application of a simple model to analyse data on water-charging systems from these two regions. We present the results of a detailed scenario-based investigation illustrating the differences between experience, composition and basis, impact and constraints on the application of water charges for both regions. The key findings are that existing water charges do not provide incentives for users to use water efficiently and thereby do not contribute effectively to the environmental objectives of the Water Framework Directive.