Water critical infrastructures (CIs) are essential for human society, life and health and they can be endangered by physical/cyber threats with severe societal consequences. To address this, STOP-IT assembles a team of major Water Utilities, industrial technology developers, high tech SMEs and top EU R&D providers. It organizes communities of practice for water systems protection to identify current and future risk landscapes and to co-develop an all-hazards risk management framework for the physical and cyber protection of water CIs. Prevention, Detection, Response and Mitigation of relevant risks at strategic, tactical and operational levels of planning will be taken into account to generate modular solutions (technologies, tools and guidelines) and an integrated software platform. STOP-IT solutions are based on: a) mature technologies improved via their combination and embedment (incl. public warning systems, smart locks) and b) novel technologies whose TRL will be increased (incl. cyber threat incident services, secure wireless sensor communications modules, context-aware anomaly detection technologies; fault-tolerant control strategies for SCADA integrated sensors, high-volume real-time sensor data protection via blockchain schemes; authorization engines; irregular human detection using new computer vision methods and WiFi and efficient water contamination detection algorithms). STOP-IT solutions are demonstrated through a front-runner/follower approach where 4 advanced utilities, Aigües de Barcelona (ES), Berliner Wasserbetriebe (DE), MEKOROT (IL) and Oslo VAV (NO) are twinned with 4 less advanced, but ambitious ones, to stimulate mutual learning, transfer and uptake. Building on this solid basis STOP-IT delivers high impact through the creation of hands-on training, best practice guidelines, support for certification and standardization as well as by fostering market opportunities, also leveraging the EU water technology platform's multi-stakeholder network.