Most wells in valley bottoms are adequate for domestic supply; however, the volume of groundwater available becomes progressively less on hillsides and ridges. Quite a few high-volume wells (more than 100 gallons per minute) are found along the Ohio River alluvium in northern Boyd County. The alluvium along the Big Sandy River also can provide adequate water for domestic use, but often contains large amounts of iron. In the southern and western half of the county, salt water may be found less than 100 feet below the level of the East Fork of the Little Sandy River valley bottom. Most of the water from drilled wells in the county, other than that from wells drilled in the river alluvium, is extremely hard and contains noticeable amounts of iron. A few springs supply enough water for domestic use. Almost all springs yield less than 5 gallons per minute.