Hi Kelly
I always just changed the formula straight off with my son, as advised by my Health Visitor . Most juice is recommended for 4 months and over, unsure why, but I gave my DD it from 14 weeks and my HV said it was fine also. I think their thinking (the manufacturers) is that no additional fluids are required until 4-6 months when solids are introduced. Don't know if that is really the reason, just what I think they think!!! My DD never drank water but loves her juice, is that why you want to give juice?