a water softening device is provided with a waste storage tank for receiving waste liquid , such as hard water used to draw out brine from a brine storage tank , as well as the used brine itself during a regeneration cycle . the tank outlet communicates with a sprinkler system , and when the sprinkler system is on , an injector valve sucks waste liquid from the waste tank to mix it in with the sprinkler system water and thereby further dilute the liquid . a method of processing the waste water accordingly includes collecting this waste liquid and preferably mixing it in with the sprinkler fluid . the brine waste and brine supply tanks in one embodiment are preferably formed as one unit with two separate compartments . the inlet pipe to the brine waste compartment has an overflow safety valve which senses , through a float mechanism , when the tank is substantially full . the valve has a normally closed port connected to a leach line or the like . this normally closed port opens when the substantially full condition is sensed , while the normally open port leading to the interior of the tank closes , so that incoming waste water passes through the valve to the leach line without changing the water level in the tank .