Thames Water has announced a hosepipe ban affecting 10.1 million customers after an “exceptionally warm and dry spring”.
The restrictions mean, from Thursday, hosepipes should not be used for watering gardens or allotments, cleaning cars, filling paddling pools or swimming pools, or cleaning windows.
The water company said its region had seen 40% of average rainfall and more days at or above 34C this year than ever recorded before.
Nevil Muncaster, director of strategic water resources, said: “We would not be taking this step unless it was necessary to protect water supplies for everyone and the environment.”
The ban applies to all customers that Thames Water supplies with drinking water and comes into effect on Thursday.
The company provides water customers across parts of Gloucestershire, Wiltshire, Surrey, the Thames Valley, Greater London, and the surrounding areas, external.
It provides water and wastewater services to 16 million customers overall.
It said water use was currently 10% above normal in the Thames Valley and Home Counties and 7% above normal in London, which amounted to an extra 100 million litres of water every day.