Diffuse water pollution from agriculture (DWPA) is a major environmental issue worldwide causing eutrophication, human health problems, increased water treatment costs and reducing the recreational potential of water bodies. In addition to penalties and provision of incentives, policy efforts are increasingly focusing on raising land managers’ awareness regarding diffuse pollution under the expectation that this would influence behaviours and thus increase uptake of best management practices that would, in turn, improve water quality. Given the multimillion financial investments in these awareness-focused approaches, a good understanding of the awareness–behavioural change–water quality pathway is critical to set the basis for assessing the real potential of these policy interventions. We systematically review the evidence across the full pathway drawing on published peer-reviewed papers from both the social and natural sciences, with a focus on Europe and North America. Results indicate that there is no one study that looks at the pathway in full, evidencing the paucity of research on the topic. For the limited studies that focus on the different components of the pathway, we find mixed evidence for the relationship between awareness and behaviour, and behavioural change and water quality. Furthermore, complexity within the pathway (e.g., through the study of factors mediating and moderating such relationships) has hardly been addressed by the literature. An in-depth understanding and analysis of this complexity—through an integrative model covering the entire pathway—could help in the design and implementation of effective policy strategies to encourage best land management practices and ultimately improve water quality.