Are you sure that your cat is not diabetic? We have an older cat, and the weak back legs and hovering over the water bowl are similar symptoms. Our cat gets daily insulin injections now and doing much better. He actually went into remission for a while and did not need the insulin. Strength has returned to his back legs. We feed him Purina M/D cat food, Evo grain free cat food and canned food at least once a day. If possible, you should try to get your cat completely off dry food and stick with the high quality canned food as much as possible.