The article said the dog was in a house and the rescuers hoped to find people alive. Perhaps there was water within the house that the dog could drink.
The pictures showed the dog clinging to the ROOF of a house, floating in the ocean. I merely question the possibility of this story being true, and find it implausible.
Dogs, cats and humans cannot drink sea water and remain alive. That dog had to have access to fresh water; and he didn't survive for 3 weeks without fresh water ....