The collective water supply system (CWSS) is part of the critical infrastructure of urban agglomerations, the efficiency of which is crucial for the security of the state and its citizens. During crisis situations, such as technical failures, contamination, natural disasters or acts of terrorism, there is a need to launch alternative water supply methods. Ensuring the continuity of water supply in crisis conditions requires appropriate preparation for such an event, estimating the real demand for water, indicating emergency water sources and providing appropriate means for its distribution. The NIK report of 2023 on ensuring the security of water supply to selected local government units in the event of crisis situations indicates that Polish municipalities are not prepared for crisis water supplies due to the lack of appropriate resources and means. The paper proposes the possibility of using water stored in the water network tank to ensure water supply in emergency situations.