Method for the operation of a water softening installation , wherein the water softening installation comprises - a softening device , in particular comprising at least one container containing an ion exchange resin , - a storage vessel with regenerant solution , wherein solid regenerating salt for the preparation of the regenerant solution is stored in the storage vessel , and - a weighing device for the determination of the weight of the storage vessel including its contents; wherein in a regeneration cycle for the regeneration of the softening device , regenerant solution is extracted from the storage vessel and conveyed into the softening device , and wherein the weight of the storage vessel including its contents is determined using the weighing device , characterised in that the water softening installation has a device for the detection and/or adjustment of a liquid level in the storage vessel, wherein during the regeneration cycle , regenerant solution is extracted from the storage vessel at least once and water is fed into the storage vessel at least once, so that the liquid level in the storage vessel does not change overall and at the end of the regeneration cycle , the same liquid level is attained in the storage vessel as at the beginning of the regeneration cycle , and in that a quantity of salt M RZ used for regeneration in this regeneration cycle is determined according to the difference in the masses of the storage vessel including its contents at the beginning of the regeneration cycle and at the end of the regeneration cycle by determining, using the weighing device , a total mass decrease over the regeneration cycle , which is based on the difference in density between the extracted regenerant solution and the replenished water. - a softening device , in particular comprising at least one container containing an ion exchange resin , - a storage vessel with regenerant solution , wherein solid regenerating salt for the preparation of the regenerant solution is stored in the storage vessel , and - a weighing device for the determination of the weight of the storage vessel including its contents; wherein in a regeneration cycle for the regeneration of the softening device , regenerant solution is extracted from the storage vessel and conveyed into the softening device , and wherein the weight of the storage vessel including its contents is determined using the weighing device , characterised in that the water softening installation has a device for the detection and/or adjustment of a liquid level in the storage vessel, wherein during the regeneration cycle , regenerant solution is extracted from the storage vessel at least once and water is fed into the storage vessel at least once, so that the liquid level in the storage vessel does not change overall and at the end of the regeneration cycle , the same liquid level is attained in the storage vessel as at the beginning of the regeneration cycle , and in that a quantity of salt M RZ used for regeneration in this regeneration cycle is determined according to the difference in the masses of the storage vessel including its contents at the beginning of the regeneration cycle and at the end of the regeneration cycle by determining, using the weighing device , a total mass decrease over the regeneration cycle , which is based on the difference in density between the extracted regenerant solution and the replenished water. <EOS>