Put water in his kibble, just enough to make it float. You will probably need to divide his food into two portions, morning and afternoon/early evening, so the water + kibble doesnt bloat his belly.
Edit:
Oh .. forgot to add.... maybe put a few ice cubes in his water bowl... see if he likes that... or what kind of bowl is his water in.. maybe he doesnt like the taste if its plastic. Or... maybe he is drinking all his water needs from some other source, water gathered in puddles, lawn furniture, or the ever popular toilet!