Answer:
You need to get a the cat to the vet immediately! The cat will surely die if not treated quickly. The quicker the cat is checked over, the better the chance of catching kidney failure in its early stages, increasing the chance of lengthening the cat's life for a while.
Your vet should tell you to give kitty distilled water and a wet, high protein, low phosphorous and carb diet. If the cat still has one good kidney, you need a specific care and feeding plan from the Vet. Call as soon as possible, please.