"Mortality from cholera in districts supplied by water companies"

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Page 1 of the Weekly Return of Births and Deaths in London for the week ending 26 November 1853.

The table at the bottom of the first page makes it clear that a population of over 300,000 people in South London were served by two water companies still in active competition. This area constituted the inter-mixed watersheds of the Lambeth and Southwark & Vauxhall (S&V) water companies. This return, however, did not appear until the 1853 cholera epidemic was in its fourteenth week, too late for Snow to begin inquiries.

He had no idea at this point if such an opportunity to add supporting evidence for his theory of the communication of cholera would reappear the following year. If cholera did not come in 1854, S&V would likely have shifted its supply source from Battersea to purer Thames water drawn above the Tedington Lock before the next visitation. There was no natural experiment if both companies provided essentially the same quality of water.]