The Medway and its tributaries and sub-tributaries have been used for over 1,150 years as a source of power. There are over two hundred sites where the use of water power is known. These uses included corn milling, fulling, paper making, iron smelting, pumping water, making gunpowder, vegetable oil extraction, and electricity generation. Today, there is just one watermill working for trade. Those that remain have mostly been converted. Such conversions include a garage, dwellings, restaurants, museums and a wedding venue. Some watermills are mere derelict shells, lower walls or lesser remains. Of the majority, there is nothing to be seen. A large number of tributaries feed into the River Medway. The tributaries that powered watermills will be described in the order that they feed in. The mills are described in order from source to mouth. Left bank and right bank are referred to as though the reader is facing downstream. This article covers the tributaries that feed in above Penshurst. West Hoathly Stream A stream rises at West Hoathly and enters from the right bank shortly before Mill Place Mill. Gravetye Foundry A gun foundry stood at Gravetye. The pond remains. East Grinstead Stream A stream flows through East Grinstead, and enters from the left bank shortly before Brambletye Mill. Brook Mill This was the manorial mill to Imberhorne Manor. Dunnings Mill TQ 391 368 Dunnings Mill was a corn mill, records date back to 1713, but the site could be earlier. The mill was demolished in the early years of the twentieth century, and the site was marked in 1932 by the sluice gate. A pub stands on the site, with a modern waterwheel. Hartfield Stream A stream flows through Hartfield, entering the Medway from the left bank downstream of the B2026 bridge. It powered four watermills. Bower Forge TQ 441 384 This forge may have been in existence in 1558, when Hugh Bottinge left "two tons of yron" in his will. It was working in 1653 but ruined by 1664. The dam has been recorded as long. The mansion of Hammerwood takes its name from this forge. Cansiron Furnace, Hartfield TQ 453 383 This was a furnace and forge mentioned in 1563. It was in operation from 1574 to 1700. Michael Weston was the ironmaster in 1574 and in 1578 it passed to William Bowyer. Richard Stretfield was the ironmaster here in the late 16th century, later