evidence: Babies under six months only need breast milk or infant formula, even in hot weather. Giving your baby water at this age may mean they drink less breast milk or infant formula. Around six months of age is a good time to start to offer small amounts of cooled boiled water in a cup. This can take some practice. Start with small amounts of water while your baby gets used to holding a cup. [...] Water given to babies to drink should be boiled to make it safe: