No city can survive without water, and lots of it. The Mercenary River tells a tale of remarkable technological, scientific and organisational breakthroughs; but also a story of greed and complacency, high finance and low politics. Nick Higham uncovers the extraordinary story of how one Victorian London water company deliberately cut off 2,000 households, even though it knew they had no alternative source of supply; the details of a financial scandal which brought two of the water companies close to collapse in the 1870s; and finally asks whether today's 21st century water companies are an improvement on their Victorian predecessors.