Thames Water has announced it is planning to introduce a hosepipe ban.
The firm supplies 10 million people across parts of southern England, including London.
The company said it was planning to announce the temporary ban "in the coming weeks" but the timing is yet to be confirmed.
It comes as a new heatwave nears and the Met Office has issued an amber extreme heat warning for much of England.
In a statement Thames Water said: "Given the long term forecast of dry weather and another forecast of very hot temperatures coming this week we are planning to announce a temporary use ban in the coming weeks."
The ban would be the third implemented in England this year, following Southern Water's ban which began last Friday in Hampshire and the Isle of Wight.
South East Water will introduce similar restrictions across Kent and Sussex from 12 August. The Isle of Man has also had a ban in place since July.
Thames Water added: "Our aim is always to ensure that we will have enough water to supply our customers, regardless of the weather."
The statement explained the firm is not able to give an exact date for the start of the ban, due to "a number of operational and legal procedural requirements" and added that in the meantime customers were being urged to "only use what they need for their essential use."
Thames Water provides water to 10 million people in an area that covers parts of London, Surrey, Berkshire, Oxfordshire, Wiltshire and Kent.
Temperatures are set to reach up to 35°C (95°F) in some areas this week.
The Met Office has issued a four-day amber extreme heat warning which applies to southern and central England and parts of Wales from midnight on Thursday until Sunday.
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