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. 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.
Route
The Whitewater rises as a series of springs and channels near Bidden, in the Odiham Fen Site of Special Scientific Interest (SSSI). The underlying chalk aquifer supplies base-rich water which encourages the growth of fen vegetation, notably lesser tussock-sedge and giant spearmoss. Almost immediately, the channels form into a pond called Mill Head, which formed part of the infrastructure for Greywell Mill. The small mill building, with an attached house, is a grade II listed structure. There are further springs and channels as the river heads north eastwards, to reach Deptford Bridge. Close by is the eastern portal of Greywell Tunnel, a tunnel built in 1792 for the Basingstoke Canal. The portal was restored in 1975, and although the canal is now navigable almost to its entrance, the tunnel is unlikely to be restored, as part of the roof collapsed, it has been colonised by a large number of bats, and the M3 motorway has been built over the original route beyond the tunnel. Beyond Deptford Bridge, there are two weirs, and Greywell Pumping Station stands on the right bank. This has extracted groundwater from the underlying chalk aquifer for use as drinking water since the early 1900s. Around 6 to 7 Ml per day are extracted, and in 2012 a study was carried out to see what effects the extraction was having on the Odiham Fen SSSI. There is a second part of the SSSI beyond the pumping station.
The canal crosses over the river on an aqueduct, and the river curves around the edge of Odiham Castle. Only a small part of the grade I listed octagonal keep, construction of which may have been for King John, remains. It was built between 1207 and 1212, and the grounds of the moated site are a scheduled monument, although parts of the earthworks and moat were damaged when the Basingstoke Canal was built. To the east of the castle is the site of Castle Mill, a ford where Mill Lane crosses the river, and then the mill pond for Warnborough Mill at Warnborough Green. The mill itself consisted of two storeys and an attic, with a two-storey house attached. It dates from the 18th century, and has been converted into a restaurant. Just beyond the tailrace the river is crossed by the B3499 Hook Road, and the A287 road, with a weir between the two bridges. Several more weirs follow, as the river threads its way between Lodge Farm on the right bank, the core of which is a grade II* listed timber framed hall-house, dating from the 15th century, and the site of a Roman villa on the left bank. Next comes Poland Mill, a large two-storey 18th century rectangular building, which originally had six water wheels, of which one with a cast iron frame remains.
The next section, which follows a more northerly course, is marked by bridges carrying the M3 motorway, the South West Main Line railway and the A30 road over the river, to the east of Hook. Beyond them is Hook Mill, with two storeys and an attic, and an attached house with two storeys. They date from the 17th and 18th centuries, and both now form part of a single house, in which the huge timbers of the mill building are still visible. Dipley Bridge carries a road over the river at the hamlet of Dipley, beyond which is Dipley Mill. The building is predominantly 18th century with modern additions, but clearly has earlier origins. After Mattingley Clappers Bridge there is a long rural section where a stream from the lake in Highfield Park joins the left bank, but there are no road crossings until the B3011 road is reached at Holdshott Farm, near the village of Hazeley. Holdshott farm house is a late 18th century building with two storeys and an attic. A timber-framed mill adjoins the north end, but it has been extensively renovated, and the cladding is modern.