Thought you might like to know what I found for you:

P.S. Fun to see you at the park!

Breastfeeding babies do not need extra water, though formula-fed babies often do. Your breastmilk contains enough water for your baby, even in hot, dry climates. Formula contains higher concentrations of salts and minerals than breastmilk does, so that extra water is often necessary for the kidneys to excrete the extra salt. Also, because of less efficient metabolism, formula-fed infants lose more water. In breastfed babies, not only is extra water unnecessary, giving bottles of water to quench baby’s thirst may also lessen the desire to breastfeed. This will interfere with the balance between mother’s milk supply and baby’s demand. Bottles of water are also likely to cause nipple confusion. A baby who is too warm or thirsty, but not hungry, can satisfy his need for more water by feeding more frequently and just enough to get the watery foremilk, but not necessarily the creamier hindmilk. Breastfeeding babies are great self-thirst-quenchers.