Cat Always Drinks An Oddly Large Amount of Water?!

I agree with evelynmcgregor in that I think your cat may have diabetes. It is a disease that can crop up in many different types of animals especially if your cat is elderly or overweight. I would take your cat to the vet immediately. Diabetes can be just as damaging in cats as in humans so it is vital that you get him checked out. The vet can rule out any health problems if it is not diabetes and may be able to give some advice regardless of the diagnosis.

I actually knew a cat parent who's cat had diabetes. He couldn't put her to sleep because of his wife so he was constantly cleaning the litter box and giving the cat water. He also had to give his cat insulin everyday. I guess it's a manageable condition but if it is diabetes it is probably pretty costly. If your cat is 16 then maybe you should just wait it out or find some better cat food (one that does not contain fillers and by products). I still would personally recommend taking him to a vet.