A new study of tens of millions of groundwater wells around the world, including New Zealand's, reveals one in five could run dry if underground water levels fall by just a few metres. Globally, shallow groundwater wells provide 40% of water needed for irrigation. They also provide tap water for homes in rural areas and cities. In areas where safe and clean water levels are declining, people may have to turn to alternative sources of water. The study done at the University of California and published in Science maps roughly 39 million wells in 40 countries, and points to the importance of building deeper wells to mitigate future expected changes in groundwater levels, and protect them from running dry. Research already carried out in New Zealand to this has been used in this study. Kathryn is joined by lead author Scott Jasechko, based in Santa Barbara, whose expertise is mapping global water quality and availability. Also Abby Matthews, a New Zealand groundwater scientist and Director of Environmental Quality at Taranaki Regional Council.