I did that with Matilda at that age, I started decreasing the milk in her bottles until we got to 50mls and then I started diluting it as well. So it would be half water and half formula. Now at almost 3 she still wakes up and asks for a bottle and we get her 50mls milk to 50mls water... its mainly a comfort thing with her, but also she gets thirsty... I guess I figure its an easy way to get her back to sleep rather than fight with her and make everyone unhappy. However, if she wakes up more than once at night, she doesn't get another bottle now. She gets a small glass of water & then back to bed.