A waterbed, water mattress, or flotation mattress is a bed or mattress filled with water. Waterbeds intended for medical therapies appear in various reports through the 19th century. The modern version, invented in San Francisco and patented in 1971, became a popular consumer item in the United States through the 1980s with up to 20% of the market in 1986 and 22% in 1987. By 2013, they accounted for less than 5% of new bed sales.