My Cat Is Sleeping More, Drinking Lots Of Water And Not Eating Much? He Is 5yrs Old. Do You Think He Is Ill

I cannot diagnose something like that over the internet.  Your best bet is to take your cat to a vet.  The vet has been trained to take care of our animals, and can do tests to see if he is ill, and what the problem is.  Then you can properly treat your cat.

Could be diabetes, I would take him to a vet immediately.

This could be signs of organ failure or diabetes, or thyroid,kidneys.See a vet. For the proper diagnosis and treatment.