To understand recommendations on whether to sterilize or not, it is important to realize the history of why sterilization was necessary in the past. In the 17th and 18th century there was a very high mortality rate for infants fed cow's milk. When pasteurization became available, technology allowed for sterile condensed milk to be used for infant feeding. However, during this time, the public water supplies remained largely unmonitored and formula was usually made in batches and left unrefrigerated, Thus, bacterial contamination tended to be a problem. Therefore, it became commonplace to sterilize the water, bottles and nipples. However, by the 1950s, city water supplies became much better monitored and free of bacterial contamination.

Studies were done back in the 1950s, which showed that babies could be safely fed formula made with clean (not sterile) bottles/nipples and tap water. However, by then, sterilization was so commonplace that it was difficult for doctors to stop recommending the practice to their patients, and it was also difficult for grandmothers to stop recommending it to their daughters.

In summary, formula prepared with city-treated tap water in the U.S. is as safe as sterilized formula. United States water from wells, cisterns or other sources should probably be sterilized by boiling for at least 10 minutes, plus one additional minute for every 1,000 feet of your city's elevation.