Our pediatric dentist recommended milk only with meals because the milk sugar on teeth all day can be a problem. He recommended only giving milk in an open cup, the reason being that we are less lenient with open cups...we let them carry around sippy cups, but open cups must be at the table (or in the kitchen, or whatever your rule). So, if you make a new "open cup for milk and open cups only at the table" rule, he may lose a bit of interest because he doens't want to be stuck at the table drinking instead of playing ?? Maybe not, maybe he loves milk enough he's sit there and drink it all 6 times a day....but it's worth a try. As with any major change for a toddler, I'd expect a few days of "disagreement" on the new rule, but it shouldn't take long before he accepts it.
One more thing, to encourage more water drinking, (we found by accident), DS loves water with a tiny squeeze of lemon juice, just enough to taste. he calls it "lemonade" and truely believes it's a big treat. the same with water with ice. a big hit.
