acre-foot

The volume of water needed to cover one acre of land to a depth of one foot — 325,851 gallons. The standard unit for measuring water supply in the American West, where every drop is allocated, adjudicated, and fought over. An acre-foot is roughly what two households use in a year. The word yokes an area to a depth, a surface to a volume, and treats water as a solid block that can be measured, stored, bought, and sold.