In Slovenia, the system of harmonized data and other information on water and water related areas is being developed as a support tool for water management planning. The system includes verified data and aggregated and logically integrated information on the state of waters in Slovenia, the pressures and impacts on water environments, and their protection. National information evidence and monitoring systems provide the data sources. The concept has been developed by way of a prototype. The system consists of independent data, organized by information themes with the logic of geographic information systems and prepared for browsing with intranet and internet.