You might want to try googeling "Feline Instincts". They have a renal powder for cats that you mix in with their food. My kitty had renal failure and lived to be 20 by taking it with little or no manuel hydration. I think they also have one for dogs.
Even if the kidney situation resolves, this might be a good idea at least for awhile.
Personally, I would not rely on vets alone. Use them, yes. Rely on them, not so much.