Is RO water safe for preparing infant formula, or does it need to be boiled?

RO (reverse osmosis) filtration removes particulates and some contaminants but does not sterilize water, and does not reliably eliminate bacterial contamination the way boiling does. For infant formula preparation, water should be boiled and cooled to about 70°C (158°F) before mixing, regardless of whether it has already passed through an RO filter — commercial formula powder is not sterile, and hot water helps neutralize potential contaminants such as Cronobacter sakazakii.

The practical protocol is to boil water, let it cool for no more than 30 minutes so it stays above 70°C, mix the formula, then cool the prepared bottle further before feeding and test the temperature on your wrist. RO filtration combined with boiling is fine; RO filtration alone is not a substitute for boiling.