You might look into a low ash cat food, such as Iams and Science Diet. Years ago when our cat had a UTI we found out this was one of the ways to control it. It might like the water bed because its cold there and that makes it easier to go.
Also there is a spray called Feelaway (sp) you can get at most pet stores that the cats can't stand the smell of.
We feed all our cats (4) Purina senior formula. It's easy to find and not expensive. Two of our cats are going on 16 without problems. One of them had UTI problems before we switched.
Purina also makes a line of canned foods labeled special diet.
It's tempting to go for the exotic foods, but Purina actually tests all its foods on animals. They devote a lot of money to research.
Thanks for the tip. My cats have only had Iams as their diet.