Caitlyn A Hall , Sheila M. Saia, Andrea Popp, Nilay Dogulu , Stan Schymanski, Niels Drost , Tim van Emmerik , Rolf Hut 

Hydrologic research that is open, accessible, reusable, and reproducible will have the largest impact on the scientific community and broader society. While more and more members of the hydrology community and key hydrology organizations are embracing open science practices, technical (e.g., limited coding experience), resource (e.g., open access fees), and social (e.g., fear of being scooped) challenges remain. Furthermore, there are a growing number of constantly evolving open science tools, resources, and initiatives that can seem overwhelming. These challenges and the ever-evolving nature of the open science landscape may seem insurmountable for hydrologists interested in pursuing open science. Therefore, we propose general Open Hydrology Principles to guide individual and community progress toward open science. To increase accessibility and make the Open Hydrology Principles more tangible and actionable, we also include the Open Hydrology Practical Guide. We aim to inform and empower hydrologists as they transition to open, accessible, reusable, and reproducible research. We discuss the benefits as well as common challenges of open science and how hydrologists can overcome them. The Open Hydrology Principles, Practical Guide, and additional resources reflect our knowledge of the current state of open hydrology; we recognize that recommendations and suggestions will evolve and expand with emerging open science infrastructures, workflows, and research experiences. Therefore, we encourage hydrologists all over the globe to join in and help advance open science by contributing to the living version of this document and by sharing open hydrology resources in the community-supported repository (https://open-hydrology.github.io).