Retrospective studies have identified alcohol as a significant risk factor in drownings involving young adults. Few studies have explored this issue, therefore the current contextual understanding of alcohol consumption in aquatic settings is limited. This study used a survey (n = 182) and one-to-one and small group interviews (n = 23) to investigate knowledge and attitudes of United Kingdom and Australian young adults (aged 18–24 years) towards involvement in aquatic activity after consuming alcohol. Findings illustrated a poor level of general and aquatic-specific alcohol knowledge. Australian educated participants, and those self-reporting: stronger swimming competence; and/or completion of alcohol and water safety education; and/or participation in aquatic activity following alcohol consumption, achieved significantly higher knowledge scores. Most reported a neutral attitude, and those with previous experience of alcohol consumption in aquatic settings had more accepting attitudes of this behavior (p < 0.001). The aquatic activity, context and amount of alcohol consumed influenced attitudes. Participants reported a lack of alcohol-focused drowning prevention or water safety education for their age group, and many referred to their upbringing and parents’ behaviors as reference for what was safe. Drowning prevention practitioners should consider these results to ensure young adults understand the risks of consuming alcohol in all aquatic contexts.