Method for operating a water softening system, comprising - a softening device, in particular comprising at least one container with ion exchanger resin, - a storage vessel, in which a regenerant solution is stored, in particular wherein in the storage vessel also solid regeneration salt is contained, - an injector, for a transport of regenerant solution from the storage vessel to the softening device, wherein a drive water volume flow of raw water from an inflow is supplied to an injector and this drive water volume flow carries away regenerant solution via a pipe, whereby a mixed water volume flow, which contains diluted regenerant solution, is received in a pipe and supplied to the softening device; - an electronic control device, wherein in a regeneration mode a pumping of the regenerant solution from the storage vessel into the softening device is activated, characterized in that in the regeneration mode during pumping of the regenerant solution in a pumping step - a volume V1 or a mass m1 of pumped regeneration solution is pre-set or measured, - and a period of time t1 for the pumping of the volume V1 or the mass M1 is pre-set or measured, and that the electronic control device determines with a stored calibration function, in particular comprising one or more stored characteristic calibration curves, a concentration C RM1 of the pumped regenerant solution and/or a parameter depending on the concentration of the pumped regenerant solution, in particular an amount of salt SM1 contained in the pumped regenerant solution, which is determined from V1 or M1 and/or from t1 (116,118; 140), wherein the calibration function uses the relationship between the pumping capacity of the injector and the density ratio of regenerant solution to drive water. - a softening device, in particular comprising at least one container with ion exchanger resin, - a storage vessel, in which a regenerant solution is stored, in particular wherein in the storage vessel also solid regeneration salt is contained, - an injector, for a transport of regenerant solution from the storage vessel to the softening device, wherein a drive water volume flow of raw water from an inflow is supplied to an injector and this drive water volume flow carries away regenerant solution via a pipe, whereby a mixed water volume flow, which contains diluted regenerant solution, is received in a pipe and supplied to the softening device; - an electronic control device, wherein in a regeneration mode a pumping of the regenerant solution from the storage vessel into the softening device is activated, characterized in that in the regeneration mode during pumping of the regenerant solution in a pumping step - a volume V1 or a mass m1 of pumped regeneration solution is pre-set or measured, - and a period of time t1 for the pumping of the volume V1 or the mass M1 is pre-set or measured, and that the electronic control device determines with a stored calibration function, in particular comprising one or more stored characteristic calibration curves, a concentration C RM1 of the pumped regenerant solution and/or a parameter depending on the concentration of the pumped regenerant solution, in particular an amount of salt SM1 contained in the pumped regenerant solution, which is determined from V1 or M1 and/or from t1 (116,118; 140), wherein the calibration function uses the relationship between the pumping capacity of the injector and the density ratio of regenerant solution to drive water.