Deciding how to feed a baby, whether breastfeeding or formula feeding, can be challenging for parents. One question: What kind of water should you use for making formula?

TODAY Parents asked pediatricians for the answers.

Best water for baby formula

When making formula for babies, parents have the option of using tap, fluoridated, well or bottled water. There are different factors to consider when deciding which one to use.

Tap water

Dr. Tye Winters, pediatric residency director and medical director of Overlook Medical Center Pediatric HealthStart Clinic, tells TODAY Parents that “the recommendation is to boil the water for at least 1 minute in a pan with a cover, then allow it to cool with the lid on the pan. This should be followed especially within the first 3 months of age or if the infant was born prematurely, prior to 36 weeks of gestation.”

Water from a public source in the United States is usually very high quality and can safely be used for mixing formulas, but Dr. Hillary O’Boyle, a pediatrician in Richmond, Virginia says it’s always good to check: “I would advise parents to make sure their tap water comes from a safe water source, as defined by your county health department or state environmental agency. “

Fluoridated water

Fluoridated water can be used to make formula; however, doctors say it should not be used during every feed, to prevent babies from getting too much fluoride in their body. Excessive fluoride can lead to skeletal changes in the infant over time.

Infant formula contains all the fluoride your baby needs, so using tap water for mixing, which typically contains additional fluoride, may put your infant at a slightly increased risk for something called dental fluorosis, says O’Boyle. This causes the appearance of faint white lines on adult teeth, which is not harmful, but may be a cosmetic concern. O’Boyle tells TODAY Parents that parents who live in areas with fluoridated tap water “may want to periodically use ready-to-feed (pre-mixed) formula and/or mix formula with bottled water, both of which do not contain fluoride.”

If you are using fluoridated water, the American Dental Association suggests checking with your local water company to make sure that the fluoride level is less than 0.7 parts fluoride per million parts water.

Well water

Winters says well water should not be used for formula, as it may contain harmful bacteria that can lead to life-threatening infections, especially in younger infants or babies with underlying health conditions. Distilled or purified water should be used in place of well water.

If well water is the only water source, exercise caution. Some wells have a high concentration of nitrates, which can seep in from fertilizer in the ground, putting babies at risk for something called methemoglobinemia. O’Boyle said, “Boiling the water does not solve this problem. If interested in using well water for formula mixing, the water should be tested periodically for nitrates to ensure safe levels.”

If the nitrate levels are safe, O’Brien said, “Additionally, all well water should be boiled prior to use.”

Bottled water

Virtually any type of bottled water can be safely used for mixing formula. This includes purified, distilled, deionized or demineralized water. Using bottled water is the best way to ensure the water is safe, and also has the advantage of not containing additional fluoride.

When choosing bottled water, it is important to know if the water has been fortified with additives such as fluoride or electrolytes, as this can lead to an excessive amount of electrolytes or fluoride within the infant’s body.

Regular bottled drinking water should still be boiled before using in formula, similar to tap water. Distilled or purified water can be used without having to boil the water.