With global warming, the hydrological cycle is intensifying with more frequent and severe droughts and floods, placing water resources and their dependent communities under increasing stress. Guidance and insights into the projection of future water conditions are, therefore, increasingly needed to inform climate change adaptation. Hydrological projections can provide such insights when suitably designed for user needs, produced from the best available climate knowledge, and leverage appropriate hydrological models. However, producing such hydrological projections is a complex process that requires skills and knowledge spanning from the often-siloed disciplines of climate, hydrology, communication, and decision-making. Accordingly, this paper bridges these silos, by providing detailed guidance on the important steps and best practices to develop hydrological projections that can effectively support decision-making. Using an extensive literature review as well as our practical experience as climate scientists, hydrologists, numerical modelers, uncertainty experts and decision-makers, here we provide: (i) an overview of climate change hydrological impacts as background knowledge; (ii) a step-by-step guide to produce hydrological projections under climate change that are targeted to water practitioners and decision-making applications, (iii) a summary of important considerations related to hydrological projection uncertainty; and (iv) insights to use hydrological projections and their associated uncertainty for impactful communication and decision-making. By providing this guide for water practitioners, our paper addresses a critical interdisciplinary knowledge gap and supports enhanced decision-making and resilience to climate change threats.