The Queen Mother Reservoir lies between the M4 and the M25 to the west of London. It is 475 acres (1.92 km2) in size or about 1 km in diameter - making it one of the largest inland areas of water in Southern England. It is managed by Thames Water.
This is one of a number of reservoirs to the west of London and was built in 1976. Its water is pumped from the River Thames nearby. The water improves in quality during its retention in the reservoir as solids settle and organic contaminants are adsorbed, absorbed and degraded through a combination of natural biological processes aided by sunlight and oxygenation. Water from the reservoir is treated (often using slow sand filters) before being put into supply as London tap water.