How much other food is he eating? By this point my kids were drinking about half the formula they used to but they also were eating table food and had a very balanced diet. If you feel that he is not eating enough other wise I would switch back to the bottle to make sure he is getting all the nutrients and calories that he needs.
Well ladies, he is eating three meals of table food and it's really balanced, lots of fruits, protein and veggies, but my doctor said until 1 year most important is the formula, so he eats all the formula of the 2 bottles he does get (morning and before bed) but the two other ones (noon and four) I put in a sippy and he leaves half...he can get it because he drinks half. ??
I would say switch him back to the bottle for the formula and then use the sippy cup for ice water, juice..Until he is off of formula i would use the bottle. Then when he starts on the regular cows milk just put it in the sippy and if he only drinks half of it, put it in the fridge till he wants it again so its not going to waste.