Thames Water Utilities Ltd, known as Thames Water, is a large private utility company responsible for the public water supply and wastewater treatment in most of Greater London, Luton, the Thames Valley, Surrey, Gloucestershire, North Wiltshire, far west Kent, and some other parts of England; it has a considerable local monopoly. Thames Water is the UK’s largest water and wastewater services company, and supplies 2.6 billion litres (570 million imperial gallons) of drinking water per day, and treats 4.7 billion litres (1,000 million imperial gallons) of wastewater per day. Thames Water’s 15 million customers comprise 27% of the UK population.

Thames Water is responsible for a range of water management infrastructure projects including the Thames Water Ring Main around London; the Lee Tunnel; Europe’s largest wastewater treatment works and the UK’s first large-scale desalination plant, both at Beckton. Thames Water awarded Bazalgette Tunnel Ltd the contract to build the £4.2 billion London Tideway Tunnel Infrastructure proposals by Thames Water include the proposed reservoir at Abingdon, Oxfordshire, which would be the largest enclosed or bunded reservoir in the UK.

Thames Water is regulated under the Water Industry Act 1991 and is owned by Kemble Water Holdings Ltd, a consortium formed in late 2006 and formerly owned by Australian-based Macquarie Group’s European Infrastructure Funds specifically for the purpose of purchasing Thames Water. Currently, the largest shareholders are the Canadian pensions group OMERS (23%), BT Pension Scheme (13%), the Abu Dhabi Investment Authority (9.9%), the China Investment Corporation (8.7%) and the Kuwait Investment Authority (8.5%). The name of the company reflects its role in providing water to the drainage basin of the River Thames and not the source of its water, which is taken from a range of rivers and boreholes.