In the event of crisis situations, such as natural disasters, blackouts or military conflicts, when the water supply system is damaged, there is a need to ensure water supply from alternative water source. Water supplied from an alternative source must have appropriate microbiological and physicochemical parameters, to protect the population from health risks associated with the consumption of water of inadequate quality. In crisis situations, water stored in the water network tanks can be considered as a potential source of drinking water. The main objective of this study was to perform a water supply crisis balance for urban agglomeration. The possibility of water supply was analysed, considering the physiological water demand of 2.5 l per person per day, the minimum water demand of 7.5 l per person per day and the necessary water demand equal 15 l per person per day. The performed analysis has shown that the water stored in the water network tanks will cover the demand for water in crisis situation.