This paper discusses the problem of the identification and definition of the urban agglomerations in accordance with Directive 91/271/EC. The aim of this identification is to guarantee a satisfactory level of treatment for urban wastewaters and the achievement of the quality objectives for water bodies. The methodology employed, taking into account the existing planning tools in the water service sector, has been based on official national census data, on the Water Protection Plan, on the predictions of Water Service Plans prepared by each Water Authority and on detailed indications provided by the Authorities themselves. The proposed approach, obtained with geographic information systems applications and the calculation of pollution loads, is described and tested in the Veneto region, Italy. In the final part of the paper some considerations on the results obtained are presented and discussed.