
Hello Garry, welcome to the board.
You are right to be worried with him drinking that volume of water. He may have a urine infection, so when you go to the vets take a sample of his urine in a sterile container. A jar that has been rinsed in boiling water shoud be fine. You don't say when you are going, but I would make an appointment quickly.
Let us know how you get on.
Sandra