If he doesn't drink much and is fed dry food he may not have enough moisture in his diet and could be producing very concentrated pee. Watch him when he pees and try to judge the colour. Ideally it should be pretty much colourless. The stronger the colour, the more concentrated it is and I don't think that's good for the kidneys. If it's a strong colour you might be best to take him and a pee sample to the vet, just to be on the safe side.
My oldie William, who's 14, is raw fed, so gets most of his moisture from his food, which is probably just as well because he never seems to drink much. I watch him when he pees and if it looks or smells strong I add some extra water to his raw meals for a couple of days. If his pee still looked or smelled strong after that I'd take him to the vet.