He sounds a dream!! Wish more people were like you and gave rescues a chance.

I certainly wouldn't remove his water completely, I personally wouldn't deprive any animal of fresh water being available at all times, but I would limit it to a smaller amount. Possibly he's been deprived of it previously so feels he has to take what he can when he can, that's something he will learn to stop doing once he realises he's safe and staying with you.

Personally I teach my own dogs and the fosters how to use the dog flap from day one, but obviously only if your garden is 100% secure and you are confident he cannot come to any damage if left outside alone. I don't know what I'd do without a dog flap...have one very messy house no doubt!!