FREEWAT (FREE and open source software tools for WATer resource management) is an HORIZON 2020 project financed by the EU Commission under the call WATER INNOVATION: BOOSTING ITS VALUE FOR EUROPE. FREEWAT's main result is an open source and public domain GIS integrated modelling environment (the FREEWAT platform) for the simulation of water quantity and quality in surface water and groundwater with an integrated water management and planning module. The modelling environment is designed as a composite plugin in QGIS v2.X. It comprises tools for the analysis, interpretation and visualization of hydrogeological and hydrochemical data and quality issues, also focusing on advanced time series analysis. It interfaces models related to the hydrological cycle and water resources management: flow models, transport models, crop growth models, management and optimization models. And it contains tools to perform model calibration, sensitivity analysis and uncertainty quantifications. Finally, the some additional tools are present for general GIS operations to prepare input data, and post-processing functionalities (module OAT – Observation and Analysis Tool).