Cover opened cans of liquid formula with aluminum foil and store in refrigerator. Use within 48 hours. Use cans of powder within 1 month of opening. Make sure you use it before this date has passed. Do not buy the formula if the can is damaged or the date has passed.
Some people are concerned with the quality of their tap water.
Have your water tested if you live in an old building or have well water. Let cold water run for a couple of minutes before you use it. This helps flush the system. Do not boil water for longer than 5 - 10 minutes. Too much boiling can increase the number of impurities.