a pet water fountain also encourages more drinking. Cats love well-oxygenated water. You can get one for about 30 bucks. If that is out of the budget you may get the same effect with an aquarium pump bubbling into one end of the water bowl. My vet also suggested fish oil capsules at one point.

My 2 current cats are doing fine, but my last one had a lot of problems in this area. Unfortunately he was a super-finicky lil' bugger and turned his nose up at just about everything other than plain dry kibble. I had to give him enemas at home, which did help for quite some time.