Modelling has recently emerged as an effective and efficient tool in the area of water quality monitoring with new models taking in vast quantities of data and facilitating the development of more targeted water monitoring programs. With the Water Framework Directive demanding that monitoring requirements for a list of priority substances be met, achieving ‘good’ status in all water bodies by 2015, there is a strong need for improved monitoring programmes. In order to improve future monitoring programmes by making the process more ‘targeted’ a simple risk-based model for the occurrence of priority substances in wastewater treatment plant effluent was devised. This model was developed through the collection of an extensive list of documents relating to priority substances emission factors. These included wastewater treatment licence applications, trade effluent licences, traffic data, rainfall data and census data. It was found that by relating data from each of these sources to historic occurrence data it was possible to conceptualise and develop to a model of risk of occurrence of priority substances. Validation of this model was carried out using data from a 24 month sampling plan at 9 sites in two counties in Ireland. This work has allowed for the compilation of a large dataset of emission factor and priority substance occurrence in Ireland where none previously existed. For the first time a risk-based model has been developed for Irish wastewater treatment plant effluents. Together the model and dataset can be used by policy makers and inform the development of future priority substance monitoring programmes.