Groundwater is a dynamic, finite, and vulnerable but resilient natural resource to be protected in an environmentally sustainable manner. Groundwater systems require a comprehensive understanding of climatology, geology, morphotectonics, hydrogeology, hydrogeochemistry, hydrodynamics, isotope hydrology, hydrogeomorhology, rock and soil hydrogeotechnics, and surface hydrology. Groundwater conceptual models (ground model, hydrogeological conceptual model, and numerical model)-from site investigations to regional watersheds and or global hydrological systems-based on earth systems make a major contribution to the sustainability and management of water resources. The thematic issue on 'sustainability and water resources' includes a wide variety of unique contributions in environmental hydrogeology and water-related research and practice.