Pipp Brook

The Pipp Brook is a left-bank tributary of the River Mole, Surrey, England. It rises at two main springs north of Leith Hill on the Greensand Ridge, then descends steeply in a northward direction, before flowing eastwards along the Vale of Holmesdale. It runs to the north of Dorking High Street, before discharging into the Mole at Pixham.

The Milton Brook, which rises at a tri-forked source lower than that of the Pipp Brook, is the principal tributary.

Later Course
Both the Pipp Brook and the larger River Tillingbourne drain the northern slopes of Leith Hill and the watershed between the two rivers (which runs roughly north–south, marks the boundary between Westcott (which the brook drains entirely) and much larger Wotton.

The Pipp Brook runs almost due east along its Dorking stretch north of much of the town and south of the steep scarp of the North Downs at Ranmore Common before joining the Mole at Pixham. The area around the confluence is the subject of occasional riparian (river) flooding as the rate of descent of the Mole decreases significantly and at the Mole Gap becomes or became subterranean, depending on amount of sedimentation.

The Pipp Brook itself has no sewage treatment works, few plains which it drains and as such an extremely narrow and low risk area of riparian flooding. These factors are instead present as to a few parcels of land of east Pixham sometimes considered Dorking by the national media based on a 2010s shorthand by the Environment Agency which has a 'Dorking Flood Area' comprising the sewage works, a handful of properties in Pixham and much of Brockham and Betchworth well upstream along the Mole to the east which are separated by more than a mile from Dorking and are narrowly in its post town.

Watermills
By the 19th century six grain mills stood on the river: Rookery, Westcott, Milton Court, Parsonage, Pippbrook and Pixham Mills. All were defunct by the mid-20th century when bread production was widely commercialised and the product nationally was transformed to slow its staleness. Pippbrook Mill and Pixham Mill survive and are Grade II listed buildings.

Water quality
The Environment Agency measures the water quality of the river systems in England. Each is given an overall ecological status, which may be one of five levels: high, good, moderate, poor and bad. There are several components that are used to determine this, including biological status, which looks at the quantity and varieties of invertebrates, angiosperms and fish. Chemical status, which compares the concentrations of various chemicals against known safe concentrations, is rated good or fail.

Water quality of the Pipp Brook in 2019: