Cristina Valhondo is a Ramón y Cajal researcher at the Institute of Environmental Assessment and Water Research (IDAEA-CSIC, Spain). Her research focuses on understanding and enhancing the natural processes that improve water quality during Managed Aquifer Recharge (MAR) and Soil Aquifer Treatment (SAT), with the ultimate goal of increasing groundwater resources and supporting sustainable water management. Her work combines hydrogeology, environmental microbiology, geochemistry and reactive transport modelling to investigate the fate of contaminants and the mechanisms governing water quality improvement in natural and engineered systems. Her research addresses a wide range of water quality indicators, including contaminants of emerging concern, nutrients, pathogens and antibiotic resistance indicators. A major focus of her work is the role of microbial communities and biofilm dynamics in the unsaturated zone, and their interactions with hydrodynamic and biogeochemical processes controlling sorption, biodegradation and contaminant attenuation. She develops and evaluates nature-based solutions, including reactive barriers and optimized recharge strategies, to enhance the performance, safety and sustainability of MAR systems.