Cat urinary tract infections are also very common. My cat is trained to use a litter box, and he has been using one since he was a kitten. When he started urinating on the floor instead of in the litter box I didn't understand what was going on. Cats have minds of their own, so I thought maybe he had just decided he didn't want to use the littler box, and he would eventually get back to using the litter box.
When he started to cry while he was peeing that's when I knew there was really something wrong with him. He sounded like he was in a lot of pain. I took him to the vet, and the vet told me the cat had a urinary tract infection. The vet told me that a good number of the cats that he sees in his office have these kinds of infections.