 The purest water in a reservoir lies between 1.5 and 3 metres beneath the water's surface, so water was extracted by means of syphons.The water now flows directly to the Arnfield Treatment Works in Tintwistle and to the Mottram Tunnel.A statutory report, prepared under the Reservoir Safety Act 1975 and dated 12 June, stated that all five reservoirs could be overtopped during a Probable Maximum Flood.