Liza Kathleen McDonough, Isaac Santos, Martin Andersen, Denis O'Carroll, Helen Rutlidge, Karina Meredith, Phetdala OUDONE, Andy Baker 

Rapid urban growth is increasing demand for potable groundwater. Dissolved organic carbon (DOC) is a major control of groundwater potability and treatment costs. We hypothesize that climate change and urbanization will not only decrease groundwater availability, but also its quality. Here, we summarize global groundwater DOC data (n = 6781) to identify its drivers and predict future changes. Our analysis of 2916 data revealed climate, dissolved inorganic ions and land use explain 31% of DOC variability, whilst aquifer age accounted for an additional 16%. Urban groundwaters were ~19% more enriched in DOC than natural or agricultural lands. We identify hotspots in the United States associated with a groundwater DOC increase of 45% by 2050, which could increase household water costs in some key regions such as Nevada, Georgia and South Carolina. Climate change will make groundwater increasingly difficult and expensive to treat, requiring more efficient and cost-effective methods for groundwater treatment in the future.