Wetlands are usually located in complex landscapes. Multiple ecosystem services delivered by wetlands to human well-being should be considered in broader contexts of wetland functions, water quality, water resource management and wetland conservation. Natural wetlands are 'kidneys' and 'sponges' of the earth that remove water pollutants and provide hydrological regulation functions vital to the environment. Where the functions of the wetlands are weakened, actions of rehabilitations are needed to revitalize those functions. While worldwide many natural wetlands have disappeared due to climate change and/or human activities, constructed wetlands, which may be seen as 'artificial kidneys/sponges' of the earth, have been increasingly built to replicate the functions of the natural wetlands. This Research Topic aims to collect and present the latest research developments in natural and constructed wetlands in relation to either water resource functions or water quality. Articles published in this Research Topic will showcase new understandings of water balances and flow patterns, vegetation characteristics, and pollutant transformations in wetland systems; innovative designs and efficiencies of wastewater treatment wetlands; and technologies that revitalize the ecosystem functions of natural wetlands. These articles are expected to bring benefits to research communities, water and wastewater industries, and government agencies that deal with wetland water management and conservation. High-quality Original Research and Review articles in this field are all welcome for submission to this Research Topic. Research interests include but are not limited to the following areas: 1. Water balances and flow patterns in natural wetland systems. 2. The hydrological regulation functions and importance of natural wetlands in their environmental context. 3. Vegetation characteristics of natural wetlands and their functional importance in wetland water pollution control. 4. Techniques for the rehabilitation of degraded wetlands. 5. The role of constructed wetlands in wastewater treatment. 6. Innovative designs and efficiencies of wastewater treatment wetlands. 7. The modeling of hydrological and/or pollutant dynamics in wetland systems. 8. The ecohydrology of wetlands. 9. The role of wetlands in the global carbon cycle. 10. Impacts of climate change and human activities on wetland hydrology and water resources. Recognizing that hydrological and biogeochemical processes are basically coupled in wetlands and their landscapes, manuscripts that report their interactions are particularly welcome.