Re drinking a lot
Ask your vet about the kidneys. I have just lost my beloved cat( last week) he was ten year old. Ever since he was a young kitten he drank a lot - it's a long story, other things masked the symptoms, I thought he was drinking because he was on cortisone (which does make them drink) for a mouth disease.
Anyway - drinking a lot can mean he has a problem with the kidneys (there's a few diseases relating to the kidneys) .
My cat had some disease called glomer ... something, can't remember the exact name. He went through a kidney transplant this month - but he only survived two weeks after the op, picked up an infection of the liver and died in his sleep.
Hope this helps , make sure you ask your vet if it could be the kidneys that's the problem (the only way that they can tell for certain is if they take a blood test first and measure the BUN, if necessary they will then take a Biopsy)