Background: Preventing drowning in adults is a complex, multifaceted injury prevention issue. The adult drowning rate in Australia is continuing to rise. In 2023, more than half of those who drowned were aged over 45 years. While there has been a call for robust, evidence-informed drowning prevention interventions across the life course, evidence of evaluated, drowning prevention programmes for adults is lacking. For more than a decade, drowning prevention researchers and practitioners in Western Australia (WA) have worked in partnership to design and evaluate evidence-informed programmes. This paper describes formative research to develop ‘Make the Right Call’ (MTRC), an adult water safety programme in WA. Methods: A staged, mixed-methods, formative evaluation was undertaken to inform the design of MTRC. Stages: The approach involved cluster analysis of coronial data 2008–2018 ( n = 93), interviews with adults aged 45–64 years ( n = 10) and 65 years and older ( n = 15), theory mapping, survey design, content and face validity testing of a baseline questionnaire with content experts ( n = 11) and a refined instrument to collect knowledge, and data on norms and water-based activity. The subsequent MTRC programme comprised a media campaign, community swimming and safety classes, lifejacket trade-in, subsidised first-aid training and community education. Discussion: The results of each stage informed the design and evaluation of a new evidence-informed and theory-driven drowning prevention programme for adults aged 45 years and older, delivered by the peak drowning prevention agency in WA, Royal Life Saving Western Australia. An investment in mixed-methods research by the partnership added rigour and credibility to the programme and evaluation design. Conclusion: To the best of our knowledge, this is the first adult water safety programme to apply a theory-driven, evidence-informed approach to its development, implementation and evaluation. The partnership was vital in maximising and accelerating the acceptable transfer of results to enhance knowledge creation and, ultimately, the design of the MTRC drowning prevention programme.