A huge cache of fresh water found beneath the sea floor off the western coast of Hawaii’s Big Island could lift the threat of drought for people living there. From a report, submitted by reader schwit1: Eric Attias at the University of Hawaii and his colleagues discovered the reservoir, which is contained in porous rock reaching at least 500 metres beneath the sea floor, using an imaging technique similar to an MRI scan. They used a boat towing a 40-metre-long antenna behind it to generate an electromagnetic field, sending an electric current through the sea and below the sea floor. As seawater is a better conductor than fresh water, the team could distinguish between the two. They found that the reservoir extends at least 4 kilometres from the coast and contains 3.5 cubic kilometres of fresh water. Most of Hawaii’s fresh water comes from onshore aquifers, which are layers of rock and soil underground that collect water after rainfall. The team believes that this newfound reservoir is replenished by water flowing out of these aquifers.