Abstract Formula fed infants experience gastrointestinal infections at higher rates than breastfed infants, due in part to bacteria in powdered infant formula (PIF) and bacterial contamination of infant feeding equipment. The United Kingdom National Health Service (UK NHS) has adopted the World Health Organization recommendation that water used to reconstitute PIF is ≥70°C to eliminate bacteria. We used community science methods to co‐design an at home experiment and online questionnaire (‘research diary’) to explore the safety of PIF preparation compared to UK NHS guidelines. 200 UK‐based parents of infants aged ≤12 months were recruited; 151 provided data on PIF preparation, and 143 were included in the analysis of water temperatures used to reconstitute PIF. Only 14.9% (n = 11) of 74 PIF preparation machines produced a water temperature of ≥70°C compared with 78.3% (n = 54) of 69 kettle users (p