Of those on private systems, about 84 percent rely on drilled wells, 9 percent on dug wells, and 7 percent on cisterns and other sources. The primary problems with private wells in Knott County are high levels of sulfur or iron. Most wells drilled in valley bottoms and on hillsides are adequate for a modern domestic supply; however, on ridge tops, only some wells produce enough for a modern domestic supply. Wells drilled in valleys to depths greater than 200 feet may yield enough water for small municipal or industrial supplies. Ground water from most wells is considered moderately hard and contains noticeable amounts of iron. In the drainage basin of the Right Fork of Beaver Creek, salty water may be found at depths less than 100 feet below the level of the valley bottom. In the rest of Knott County, salty water in wells probably will not be found less than 200 feet below the level of the principal valley bottoms. A few springs supply sufficient quantities of water for domestic use, usually less than 5 gal/min.