Mixing formula seems simple, but the water you use really matters. Here’s what to know: If it’s tap or filtered water and your baby is under 3 months: boil it for at least 1 minute and let it cool before mixing. Choose water that’s low in minerals (under 200 mg/L sodium, under 250 mg/L sulfate). Too many minerals can be hard on little kidneys. Be cautious with bottled water! not all are baby-safe. Look for “suitable for infant feeding” on the label or stick with cooled, boiled tap water you trus