*Can a cat get dehydrated & lose it's hair?*?

We have several cats in our home! The first cat we acquired is all black and has had an on-going issue with hair loss. Over the last few months the other cats have been losing their hair as well. The hair loss is primarily on their legs and backsides. One cat did end up losing some on the sides of her belly. I first wondered if the cat with the initial issues has some kind of disease or something that causes hair loss and had ped it along to the others? One day it hit me that maybe they weren't getting enough fluids and could be losing their have because of it?! I have a vet visit scheduled for the yearly stuff in about a month. In the meantime... What do you think?