I think sometimes it helps if you raise the water bowl; and/or put ice cubes in it to slow him down when drinking water - if he is maybe drinking too fast.
maybe, is that being a stray he didn't have enough access to water and so now he is just taking as much as he can. But I would still consider another trip to the vet, as it could be the result of a health problem...
Dogs don't need to talk, their life is their message ~ unknown.
"The greatness of a nation and its moral progress can be judged by the way its animals are treated." ~ Mahatma Gandhi