I have a 14 month old who hates sippy cups. So I just put some water in his bottle with cow's milk so he can get the water he needs. For example, 6 oz of cow's milk with 2 oz of water. I don't see anything wrong with it. Just wanted to be sure though. That's fine, right? ****EDIT****** ok people. he bites down on sippy cups. bites down on straws. he'll only suck on a bottle. it's not as easy as you're making it out to be. and he hates water by itself. so this is what i resorted to. he gets lots of milk a day and good amount of water as well for hydration... all because i am mixing it together. I'm only doing what i can for my child. each child is so different.