I found that as soon as we stopped breastfeeding, and went onto formula (about 6 months), ds would get constipated if I didn't give him extra liquids as well as the formula, even though I was mixing it up right. This coincided with the introduction of solids. My HV said to class formula as a food, not a liquid, so he really should have extra. Ds has about 250ml of water a day (spread out across the day), but I think it varies from baby to baby. As long as your baby is not constipated (hard, dry stools), and doesn't show the signs of dehydration (depressed fontanelles, skin bounces back when pinched - not too hard
), then you are OK. Ask your HV what she thinks.
Welcome to the boards, and congratulations on your little cutie