<p>Water scarcity is a global concern, necessitating the exploration of alternative water resources. Effective decision-making and sustainable water management require prioritising key factors in this development process. This study comparatively analyses the distinct perceptions and priorities of South Korea and Vietnam in alternative water resource development. This comparative analysis aims to inform decision-making, resource allocation, and cross-cultural learning. Utilising the Analytic Hierarchy Process methodology, surveys were conducted with 53 experts in both countries. After excluding inconsistent responses, 40 valid responses were analysed, revealing significant disparities in the prioritisation of development criteria. South Korea emphasises environmental and social factors (weighted at 39.0%), reflecting its sustainability awareness, while Vietnam prioritises economic factors (54.9%), aligned with its development goals. Based on these distinct findings, tailored policy implications are crucial. For South Korea, the focus should be on soft infrastructure, such as transparent public engagement and robust regulatory frameworks for environmental protection. For Vietnam, policies must prioritise creating attractive financial environments, including economic feasibility guidelines and investment incentives.</p>