evidence: Health Canada recommends that infants who are premature, have a low birth weight, or weakened immune systems, drink commercially produced sterile liquid infant formula, if they're not being breastfed. [...] For premature and low birth weight infants under two months of age or infants with a weakened immune system - Boil water for 2 minutes. [...] - Remember, once you've started feeding your child, the bottle should be used within 2 hours.