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. <EOS>