I have two suggestions to try. First, add water to his food so that hopefully he will get some that way.
Second, freeze a diluted water and broth mixture into shallow ice cubes. Start giving him the cubes as treats. Look for low sodium broth and make sure you check the labels. Campbell's just came out with a really low sodium, few ingredient chicken broth. When I make them I put about 1/8 th of an inch of broth into the tray, semi freeze it and then add another 1/8 - 1/4" of water and fully freeze the combo If he likes them then start adding one to his drinking bowl in the middle of the bowl and only fill the bowl by about a half an inch. Make sure he sees and knows what you are doing. The idea is to get him to dunk for the cube and take in water as he does it. It helped me "cure" my side drinker but I have found that she prefers me to have the bowl half full - maybe she snorted some as a baby and has an aversion to putting her muzzle into deeper water, who knows? She also prefers her ceramic dish to the stainless ones that everyone else likes. Hope it helps.