Greywell Mill on the upper reaches of the River Whitewater.
The River Whitewater rises at springs near Bidden Grange Farm between Upton Grey and Greywell in Hampshire, England. It flows northeast and is a tributary of the River Blackwater near Swallowfield. Its headwaters flow over chalk and there is little pollution making the River Whitewater rich in wildlife. It was noted on Jansson's map of Hampshire of 1646.
The settlements of Greywell, North Warnborough, Hook, Hartley Wintney, Rotherwick, West Green, Mattingley, Bramshill and Heckfield lie on the River Whitewater.
The river contains a variety of species of fish including brown trout, dace, barbel, perch, pike, roach and chub. Fishing on part of the river is controlled by Farnborough and District Angling Society which has separate coarse and fly fishing sections. Like many rivers in the south of England, non-indigenous mink and signal crayfish are present.