A census from 1851 shows that in Cowm Valley some 139 people were living in farms and households scattered throughout the area. The landscape would have been similar to many of the quieter valleys in Lancashire, with hayfields on the lower slopes and grazing land on the surrounding moorlands. As well as farming, employment was to be found in the substantial quarries at the northern end of the valley, or at its two mills. Back Cowm Mill spun and weaved cotton, and Dules Mouth Mill was a stone polishing factory.
There was increasing demand for drinking water from the expanding Rochdale population, especially during the summer months. At this time of year, the lack of supply meant that water was often only available for half of the day.
In 1866, the Rochdale Waterworks Act gave the Rochdale Waterworks Company the power to impound Cowm Brook and buy land where the planned site of a reservoir would be. It also enabled them to force the discontinuation of both Dules Mouth Mill and Back Cowm Mill. This would have clearly impacted employment opportunities within the valley and started the slow process of emptying it of people.
If any further proof were needed of the necessity for the construction of a new reservoir, a three-month long drought in 1868 meant that to provide water for the town, emergency measures had to be taken. Water from mill lodges and collieries was utilised, water carts with barrels were stationed on to the streets and old water pumps were brought back into use.
Work Begins
With an Act of Parliament authorising the building of Cowm Reservoir, work began on 26th December 1868. Isle of Man farm, and the residences of Sike, Backfield and Ketley Cote were all demolished as they would be submerged by the waters. The looms and throstle spindle machines from Back Cowm Mill were sold off by Rochdale Corporation.
Construction did not proceed smoothly as the underlying rock was of a complex structure with deep fissures, both in the bed of the reservoir and under the dam. Particular care needed to be taken with the dam construction. The dam was 16 metres high and had a puddle clay core, and underneath it was a puddle clay ‘cut off trench’. A cut off trench underneath a dam is an impervious layer to prevent water from seeping through the foundations, and it also stabilises the dam. Puddle clay was a common substance used in dam construction and to line reservoirs. It is clay that is pummelled sufficiently to make sure it is watertight.
Serious Difficulties
Soon after the reservoir was filled for the first time, it was noticed that there was water leaking out. This would have caused much anxiety, with the recent memories of the 1864 Dale Dyke disaster in Yorkshire still fresh in people’s minds. On its first filling the Dale Dyke dam broke and a wall of water burst through, rampaging eight miles through villages and down into Sheffield, killing 238 people, destroying 130 houses and severely damaging 470.
Cowm’s dam’s designer Thomas Hawksley was recalled in 1879, and it was deemed the cut off trench was the cause of concern. He had had a similar problem with a dam he’d constructed at Tunstall, County Durham. There he had pioneered a concrete ‘grouting’ technique which he then used at Cowm. The rock underneath the Cowm dam was complex, with beds of sandstone and shale and deep fissures within them. Hawksley ordered holes to be bored deep into the rocks and then had concrete pumped into them. These remedial measures worked for six years, but then some discolouration of local well water and subsidence in a nearby hillside were both seen as warning signs. Further concrete grouting work was carried out, and this time it proved successful at enabling the dam foundations to become watertight.
After the First World War, the water board brought increasing pressure to move more people out of the valley, always being mindful of the possibility of a pollution episode caused by sewage. This proved a slow process though and the Parker family managed to hang on, with Jack Parker being the last to leave his home at Back Cowm Farm in 1950.
An Environmental Disaster
In July 1975. a disaster struck the reservoir. Over the years, thousands of old tyres had been stored in holes in one of the quarries at the northern end of the valley. Somehow, whether by accident or on purpose, they were set on fire. Eyewitness Joan Douglas described watching thick black smoke, rolling down the valley blotting out the sky. While attention was focused on this, a far more serious problem was occurring.
Liquid phenol leached out of the burning tyres, and flowed into a small stream, which fed into Cowm Brook and on into the reservoir. Locals began to complain that their water tasted like TCP, an astringent mouthwash. Thirty-six hours passed before the public were officially made aware that there was a problem with the drinking water. Water carts were brought in for residents. To prevent further pollution from entering the reservoir, the brook was diverted into a temporary pipeline. Sausage-like booms were put in place at intervals at the top of the reservoir, where there is a narrow neck, to collect the scum off the surface. The pollution was scooped off into drums and taken away by tankers. A swing barrier was installed at the bottom of the quarry road at Tong End, manned day and night to ensure no more tyres were brought up to the site. At the time, Cowm Reservoir was the main water supply for Rochdale, but with it out of commission, nearby Spring Mill Reservoir needed to make up the shortfall.
The reservoir and brook were completely polluted, and even into the early 1990s it could not be used for drinking water as traces of phenol continued to be found. There was speculation that it would be drained and never refilled, and the valley returned to nature, but this did not happen.
A Slow Recovery, and a New Use
In 2009, the Manchester Evening News reported that the water quality had improved sufficiently that United Utilities were considering bringing Cowm back into use as drinking water reservoir. By 2014, United Utilities were actively laying the pipe infrastructure to do this when there were complaints from locals about a bad smell, and they feared the phenol pollution had been disturbed again by the water authority’s excavation work. However, United Utilities stated that it was an unrelated diesel incident, which they were investigating.
In the same year, the Waterski Academy was set up as a social enterprise. This has proved to be very popular and is open seven days a week. As well as recreational skiing and providing training, the group also has championship waterskiers training at the facilities. At the time of writing the reservoir has been once again been deemed suitable for drinking water, and happily United Utilities state there is no conflict between this and the water skiing activity.
In recent times, the area around Cowm Reservoir has become part of the Spodden Valley Revealed project. This aims to link together historical sites throughout Whitworth. At Cowm, improvements have been made to the land around the reservoir. Paths have had vegetation cleared off them to reveal the historical stone surfaces beneath. Drystone walls have been repaired to a high standard, and drainage problems have been tackled. The whole area is now very welcoming and full of interest to both walker and historian alike.
Site visited by A. Bowden and A. Shepherd 2022
Access
There is a car park at Cowm Reservoir with a parking charge. There are no toilet facilities, but there is sometimes a pop up cafe. There is a circular walking trail around the reservoir, and public footpaths up into the surrounding hills as well.
Nearby
The James ‘Treacle’ Sanderson Monument
References
Cowm: The Valley That Died, Joan Douglas Whitworth Historical Society. This book is still in print and available from the Whitworth Heritage Museum here
manchestereveningnews.co.uk/news/local-news/cowm-reservoir-back-on-tap-935288
en-gb.facebook.com/TheWaterSkiAcademyWhitworth/
spoddenvalleyrevealed.wordpress.com/2018/06/28/the-reveal-begins-at-cown-reservoir/
midpenninearts.org.uk/programmes/spodden-valley-revealed/
Lancashire Past 
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