How much water should be given to formula feeding babies in a day?
This is a question that really depends on the EXACT age of a baby. I think this article should have all of the answers to your question, but you should definitely be mindful of each and every detail: http://kellymom.com/nutrition/starting-solids/baby-water/
Rule of thumb is to give no water for babies below 6 months of age, whether breastfeeding or not. The belief that babies need water is already obsolete.