Thames Water, which also counts residents in Fairford and parts of the north Cotswolds among the 15 million people it supplies, has become the latest water company to introduce the ban.
The announcement comes after a drought was officially declared across most of England following the driest July for 50 years and the driest first half of the year since 1976.
Despite the recent rain after the end of the heatwave, the Environment Agency has said it will take weeks’ worth of rain to replenish water sources and Thames Water said levels in its reservoirs were “much lower than usual”.
In a statement on its website, the company said said: “We have more teams reducing leakage than ever before, working 24/7 to find and fix more than 1,100 leaks every week. The recent heatwaves mean that demand for water is also at record levels.
“We’ve been working around the clock to supply everyone, and customers have been brilliant at saving water where they can. But, with low rainfall forecast for the coming months, we now need to take the next step in our drought plan. Everything we do now will help protect supplies next summer and help the environment.
“We know these restrictions impact your day-to-day activities around your home and beyond, and we’re grateful for your support.”
The ban means you cannot water your garden, wash your car, fill a pool or do anything using a hose connected to the mains water supply.
You would be able to use tap water in a bucket to water your garden or wash your car and you would also be able to use a hosepipe if it is connected to a water butt containing rainwater or greywater.
There are some other exemptions, for example if the hosepipe is being used for commercial purposes, such as car washes or watering of plants or crops being grown for sale.
Anyone found breaking the rules could be liable for a fine of up to £1,000.
More information is available at thameswater.co.uk/help/water-restrictions/legal-notice