The Slow Sand Filters
The primary function of the Pumping Station was to provide clean water to the inhabitants and businesses of Darlington and Teesside. Although the extraction of water from the Tees, upstream of these habitations, in itself provided a more healthy supply, added purification in the form of Slow Sand Filters provided an extra layer of protection. This simple process was undertaken in a large basin containing fine filter sand, supported on a layer of gravel.
In addition to removing solid matter, carried by the river water, a biological layer naturally formed on top of the sand and provided a degree of bacterial action, so further improving water quality.