L.B.
As long as he is having some good wet diapers and isnt constipated, which is common too, and nothing to worry about, then I would think he is fine. My 11 month old is drinking less too, so its a normal thing. She has been a bit constipated, so I just give her some extra water whenever I can. You cant force them to do what you want them too, I have learned that thru the years, so go with what he wants, they do know what they want and need. Good Luck!