The Stain Hill Reservoirs lie to the north of the River Thames near Kempton Park Racecourse between Kempton Park and Hampton.
The reservoirs were built by the Southwark and Vauxhall Waterworks Company and are now managed by Thames Water.
The reservoirs are no longer used for pre-treatment water storage, but are now used for the storage of wash water from the adjacent treatment works to allow the settlement of solids out of suspension. The water is then discharged to Sunnyside reservoir for further settlement before being discharged back to the river Thames.
Stain Hill has significant populations of moulting and wintering waterfowl, particularly where the water is shallow and marginal vegetation has developed. There are nationally significant numbers of shoveler and gadwall in late winter. The dry concrete banks support one of the UK's largest populations of the nationally scarce plant tower mustard (arabis glabra), a UK Biodiversity Action Plan Priority species. Other locally uncommon plants include field mouse-ear (cerastium arvense), vervain (verbena officinalis) and wild clary (salvia verbenaca).