Palau produces 300 billion gallons (1.1 billion cubic metres) of water per year from surface water run-off. The island of Babeldaob has 5 major watersheds with an additional 11 minor watersheds. The Ngerikiil River in Airai supplies 3 million gallons (11,000 cubic metres) a day to the Koror/Airai Water Treatment Plant for use by three-fourths of the population of Palau. The rest of the islands of Palau rely on groundwater sources and rainfall.