You can safely use fluoridated tap water to prepare infant formula. Exposure to fluoride during infancy helps prevent tooth decay.
However, regularly mixing powdered or liquid concentrate infant formula with fluoridated water might increase your child's risk of developing faint white lines or streaks on the teeth (fluorosis) if these kinds of formula are your child's main source of food.
Fluorosis is a cosmetic issue that affects both baby teeth and permanent teeth while they're forming under the gums. In young children, combined fluoride exposure from all sources contributes to fluorosis. This includes the fluoride in fluoridated water, foods and drinks made with fluoridated water, and fluoridated toothpaste and mouth rinses — especially if these products are swallowed. Fluorosis can't develop or worsen once permanent teeth break through the gums.
If you're concerned about fluorosis, consider ways to minimize your baby's exposure to fluoride. For example, you might use ready-to-feed formula, which contains little fluoride, or alternate between using fluoridated tap water and low-fluoride water — such as purified, demineralized, deionized or distilled bottled water — to prepare concentrated formula.
Remember, though, early exposure to fluoride helps prevent tooth decay. If you feed your baby only ready-to-feed formula or concentrated formula mixed with low-fluoride water, your baby's doctor might recommend fluoride supplements beginning at 6 months. Be sure to talk to your child's dentist or doctor about your child's other possible exposures to fluoride first.