Abstract: The invention relates to a water extinguishing system with a fluid supply for providing an extinguishing fluid, a pump which is configured to pump the extinguishing fluid from the fluid supply into a supply line of a pipe system of the water extinguishing system, a test line which branches off from the supply line of the pipe system and is configured to conduct the extinguishing fluid pumped by the pump away from the pipe system, and a fluid bypass line with a cross section reduced in comparison to the cross section of the test line, where the fluid bypass line is configured to conduct a predefined portion of the extinguishing fluid around an opening element of the test line away from the pipe system, where the water extinguishing system further comprises at least one control device which is configured to determine at least one parameter indicative of the cross-section of the fluid bypass line, and to control the pump test run of the pump on the basis of that parameter.