Okay, I'm going to assume that you mean that your water softener SALT tank is what is full of water. That most likely means that your brine draw line (the poly tube that sucks the brine out of the salt tank, usually 3/8" poly tubing) is probably cracked. Just picture it as a straw in a glass of iced tea. If it has a hole in it you will suck more air than tea. The water softener doesn't know this so it assumes that all the brine has been flushed through the system, and refills it for the next time. It fills up quickly! Replace the tube and don't bother dipping the water out of the salt tank, it will return to its normal level in a few days.