Loudwater is a village in Hertfordshire, England, near the border of the county with Buckinghamshire. It is on the north bank of the River Chess just to the east of Junction 18 of the M25 motorway, north of Rickmansworth. The name Loudwater is an old name for the River Chess. The 2001 population was 1,242, with, in 2002, nearly a quarter being millionaires, the highest concentration of any community in the United Kingdom. In the mid-19th century a paper mill was established in Loudwater using new technology developed by George Tidcombe. The mill was still standing in 2008.