Several things may help. Try moving his dinner time up a little if you can. Put his water up about 7 PM. The biggest thing would be to crate him. The dog may be
happier in its den than loose in the house. It relaxes, it feels safe in its
den. It rests, the body slows down reducing the need for water and relieving
its self. Dogs that have been crated all along do very well. Many of them
will rest in their crates even when the door is open. I think the plastic
ones give the dog more of a safe, enclosed den feeling. Metal ones can be put
in a corner or covered with something the dog can't pull in and chew. Select
a crate just big enough for the full grown dog to stretch out in.
Leave it some toys. Perhaps a Kong filled with peanut butter. Don't leave
anything in the crate the dog might chew up. It will do fine without even any
bedding. A dog that has not been crated since it was little, may take some work.
Start out just putting its toys and treats in the crate. Praise it for going
in. Feed it in the crate.
You may want to look at Housebreaking in the sticky,
http://www.askmehelpdesk.com/dogs/in...tml#post251809 If he is otherwise doing well, there may not be a lot of help for you there.