stew up a little meat or fish in loads of water, no salt and give the dog the strained juices. overcooked rice or pasta also holds a lotos water and can be given with or instead of the normal food. Can I ask why your dog needs to drink more?
I put a measure of rice into six times the measure of water with a little chopped chicken, bring to the fast boil to cook the chicken then cover , remove from heat and allow to cool. The result is a tasty very soggy rice mix that you can feed to settle the tum and rehydrated.