 The engines were housed in Staines pumping station south-west of the south reservoir.Under the original legal provisions, when the flow of the river at Bell Weir exceeded 265 million gallons a day (1.205 million m3/d) the joint company could abstract any surplus up to 100 million gallons (454,609 m3) of which 35 million gallons (159,113 m3) could be run directly to the filter beds at Hampton and the surplus (295,496 m3/day) pumped into the reservoirs.The top water level in the North Reservoir is 3 m higher than the South reservoir.