[Artie]

Thanks for the replies guys. I've had him since he was about 12 weeks and in that time he's never had tap water, only the same bottled still mineral water I drink myself. They put too many chemicals in the tap water in my opinion.
He's also only ever had Carefresh bedding, never any pine as I researched before buying him and heard it wasn't good for them.
It's really hard watching him slow down so much and sleep more and more.
@ Puddle - he actually started drinking much more around the age of 2. Before that his bottle barely went down at all in a 24 hoyur period but now it can go down a good cm or more.
@ Souffle - thanks for the protein tip as I had thought he must be lacking it to be getting thinner. He does enjoy egg white but it's something he'll nibble a very small piece of while I hold it and then just leave, knowing when he's had enough and makes no attempt to pouch any.