A fascinating wrinkle of history:
The dramatic increase of people to populate the new urban spaces of the Industrial Age may have had one other cause: tea. The population growth during the first half of the eighteenth century neatly coincided with the mass adoption of tea as the de facto national beverage. (Imports grew from six tons at the beginning of the century to eleven thousand at the end.) A luxury good at the start of the century, tea had become a staple even of working-class diets by the 1850s. One mechanic who provided an account of his weekly budget to the Penny Newsman spent almost fifteen percent of his earnings on tea and sugar. He may have been indulging in it for the taste and the salutary cognitive effects of caffeine, but it was also a healthy lifestyle choice, given the alternatives.
Brewed tea possesses several crucial antibacterial properties that help ward off waterborne diseases: the tannic acid released in the steeping process kills off those bacteria that haven't already perished during the boiling of the water. The explosion of tea drinking in the late 1700s was, from the bacteria's point of view, a microbial holocaust. Physicians observed a dramatic drop in dysentery and child mortality during the period. (The antiseptic agents in tea could be passed on to infants through breast milk.) Largely freed from waterborne disease agents, the tea drinking population began to swell in number, ultimately supplying a larger labor pool to the emerging factory towns, and to the great sprawling monster of London itself.