<p>Farmer behaviour plays a crucial role in water pollution and protection dynamics, influencing land management decisions, pollutant runoff and engagement with sustainability. The challenges associated with agricultural water pollution arise from the complex interplay of human behaviour, pollution sources, different farm systems within catchments and ecological variability. As a global issue, it poses significant risks to ecosystems, public health, and agricultural productivity, requiring an integrated approach that encompasses understanding and encouraging farmer pro-environmental behaviour. This study leverages a comparative self-perception versus other-perception framework, enhancing the reliability of behavioural evaluations while establishing crucial connections between farmer behaviour, farm characteristics, and water quality risks. The study employs the Capability-Opportunity-Motivation-Behaviour (COM-B) model to investigate factors influencing farmers’ engagement with pro-environmental water quality behaviours through a mixed-methods approach, using a novel combination of qualitative (focus groups and interviews) and quantitative (advisor-reported) assessments. Findings highlight key behavioural drivers and constraints, including motivation, knowledge, advisory relationships, and societal pressures. Notably, differences emerged across farm types and pollution pressures, with larger farms showing greater readiness to adopt pro-environmental behaviours. The study offers policy-relevant insights, including recommendations for targeted education, financial and societal supports to enhance behavioural readiness and promote sustainable water quality practices. Moreover, this study contributes to the literature by introducing methodological novelty in employing a mixed-methods approach that combines qualitative insights from farmer focus groups and interviews with advisor-reported behavioural assessments.</p>