During the 19th century, at the time of the Industrial Revolution, Birmingham's population grew rapidly. Clean water was in short supply and there were major epidemics of water-borne diseases including typhoid, cholera and diarrhoea. Birmingham City Council, led by Joseph Chamberlain, set about finding a clean water supply for the City.
James Mansergh had previously identified the Elan and Claerwen Valleys' potential for water storage; the area had :-
- An average annual rainfall of 1830mm.
- Narrow downstream valleys which made building the dams easier. Impermeable bedrock preventing the water seeping away.
- Altitude - the area is mostly higher than Birmingham enabling the water to be transported by gravity, without needing to be pumped.
The Birmingham Corporation agreed and an Act of Parliament was passed for the compulsory purchase of the total water catchment area of the Elan and Claerwen Valleys (180 square kilometres). The choice of the Elan Valley as the source of Birmingham's future water supplies was to lead to the creation of a spectacular new landscape in mid-Wales.
Water is extracted from the Foel Tower to the Severn Trent water treatment works. It is cleaned by rapid gravity filter sand beds. Chlorine, fluoride and lime (to neutralise the acidic water) are added.The Foel Tower stands 52m above the Frankley Reservoir in Birmingham. The gradient of the aqueduct which links them averages 1 in 2,300, which allows the water to flow by gravity alone.
Water is extracted from Caban Coch Reservoir for the Welsh Water treatment works which supplies the local area. An average of 360 million litres of water a day from the Elan Valley can be extracted to supply Birmingham. Once the Claerwen Dam was completed this nearly doubled the available water for Birmingham.