Are there any residential hot water tanks which tell you how much water is inside?

Question

Are there any residential hot water tanks which tell you how much water is inside?

Answer 1

Hot water tanks always have the same amount of water in them. Since heat rises, hot water is taken from the top of the tank, and cold water enters the bottom. There is no valve controlling the water entering the tank because the pressure of the incoming water forces the hot water out the top. If you shut off the input, you wouldn't be able to get any hot water out of the tank.