Thames Water

From the Wikipedia page

Thames Water Utilities Ltd, known as Thames Water, is the private utility company responsible for the public water supply and waste water treatment in large parts of Greater London, the Thames Valley, Surrey, Gloucestershire, Wiltshire, Kent, and some other areas of in the United Kingdom. Thames Water is the UK's largest water and wastewater services company, and supplies 2.6 Gigalitres of drinking water a day.

Thames Water is responsible for a range of water management infrastructure projects including the Thames Water Ring Main around London, Europe's largest wastewater treatment works[1] and the UK's first large-scale desalination plant.] Infrastructure proposals by the company include the £2.2 billion London Tideway Tunnels, and the proposed reservoir at Abingdon, Oxfordshire, which would be the largest enclosed reservoir in the UK