The story
The company was created in 1811 to take advantage of a clause in the Grand Junction Canal Act 1798 (38 Geo. 3. c. xxxiii) which allowed them to supply water brought by the canal from the River Colne and River Brent, and from a reservoir (now Ruislip Lido) in north-west Middlesex supplied by land drainage. It was thought that these waters would be better than those of the Thames, but in fact they were found to be of poor quality and insufficient to meet demand. After failing to mitigate these problems the company resolved to take its supply instead from the River Thames at a point near Chelsea Hospital.
From Wikipedia’s article on Grand Junction Waterworks Company, shared under CC BY-SA 4.0.3