hot water heaters are somewhat like a percolator, the water boils at the bottom and then rises up the thing that I cant think of the name of . to heat the water all the way to the top. so probably tthat thing is broken which can happen sometimes with wear and tear, rust, moving it . so you dont have less water just less water is being heated! Ido not know how the thing can be replaced or what ever so google it!
joey
February 2007