Thames Water has announced a hosepipe ban affecting 16 million people 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 for 16 million customers across parts of Gloucestershire, Wiltshire, Kent, Surrey, the Thames Valley, Greater London, and the surrounding areas, external.

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.

Muncaster added: “Recent heatwaves and a very dry spring and summer have led to sustained high demand. While there is enough water for essential use, we need to reduce non-essential outdoor demand to keep taps flowing.

“Many customers have already reduced their water use and that support has made a difference. Thank you to everyone who has already changed their daily habits.

“Our teams are working 24/7 to keep water moving, fix leaks and support customers. We will keep the situation under close review and lift restrictions as soon as it is safe to do so.”

The company said this year’s hot weather had meant during peak periods “water has been used faster than it can be treated and moved through parts of the network, placing additional pressure on local supplies”.

“Customers should continue to use water for essential needs such as drinking, cooking, washing and hygiene,” it said.

“Buckets and watering cans can still be used, and there are exemptions, including where water use is necessary for health and safety reasons or for customers with severe mobility problems.”

Thames Water is about £20bn in debt.

The government recently rejected a rescue proposal, and the BBC understands the company’s main lenders are preparing a legal challenge in case the new Andy Burnham-led government takes the firm into public hands.