Oklahoma has 22 major groundwater basins containing 390 million acre-feet of water, with the Ogallala Aquifer being the largest, able to store 90 million acre-feet. The state also has over 55,000 miles of surface water. However, about 500 residents in Red Rock, Oklahoma currently do not have access to clean drinking water due to high levels of silt and dirt contaminating their water supply after a flood opened a nearby dam. The State of Oklahoma oversees over 1,680 public water supply systems serving 3.7 million people. Though Oklahoma receives over 10.5 million acre-feet of water annually through rivers, which exceeds total state demand of 1.8 million acre-feet.