Water is essential to all life, and the global hydrological cycle is complex, and interconnected to human life and activities, as well as biodiversity. Quality of water needs to be regulated and managed in relation to hundreds of different chemicals coming from agriculture, wastewater treatment and other sources.  Increasingly we are seeing severe hazards arising from extreme weather events changing water quantity. There are emerging contaminants for which we as yet do not have full understanding of their distribution and impacts. Developments in new sensor technology and innovations in monitoring are transforming our ability to observe the hydrological cycle. Data relevant to the hydrological systems arise from in situ sensors, lab based field sampling and measurement and increasingly earth observation.  This area is rich for statistical and data science innovation and our speakers will present a number topics show casing the diversity of challenges.  the session will consider the common challenges of handling complex data structures, systems approaches to modelling complex water courses, developing novel approaches to quantifying and communicating uncertainties and finally explore novel tracers in human health studies.