The filtration of water in the Greenfield, Dovestones and Chew valleys is more difficult than many other sources. Not only does it have to provide clean, wholesome water but that water has to be free of discolouration and excess acidity. A big problem in this valley is the peaty water. All the water entering the reservoirs has a lot of suspended peat within it, which gives it a chocolate brownish colour and even it was safe to drink after filtration nobody would be happy with the colour of the water. Combating this at Ashway Gap Filter House were various mechanical filters and also some that required the use of chemicals to consolidate the peat and bring the acidity to neutral. Much of this is described in the attached booklet.