A review of the 1892 water demand forecast for Birmingham

The water demand forecast forms half of the supply–demand balance used for developing a long-term water resources plan, but historical water demand forecasts attracted less analytical attention than historical water supply issues. This paper is a critical review of the water demand forecast for the city of Birmingham, which was presented to Parliament by James Mansergh in 1892 – when demand was growing by 3% per annum and the headroom of supply over demand was approaching zero – to justify the need for one of the largest and most controversial water resources schemes in the UK, the Elan Valley reservoirs in Mid-Wales. The first phase was commissioned in 1904. Today, the full scheme supplies water to over a million people in Birmingham, and will continue to do so well into the twenty-first century, long after the 60 to 70 years originally expected by Mansergh. The results of this analysis suggest that by demonstrating an understanding of the drivers of demand growth, Mansergh was able to convince Parliament that his assumptions about the scale of Birmingham's future demand growth were reasonable. A comparison of the 1892 forecast with actual annual average demand up to Mansergh's horizon in 1955 shows that the profile of his forecast was remarkably accurate.