A hosepipe and sprinkler ban is being imposed on people across Kent and Sussex, South East Water has confirmed.
The firm said it "had no choice" following the driest July on record.
The measure, which comes into force on 12 August, affects at least one million people, and rule-breakers could be hit with a £1,000 fine.
It follows pleas from the water company for people to only use water for essential purposes during hot weather warnings and shortages last month.
The ban will prohibit people from using a hosepipe to water plants, wash the car or fill a paddling pool.
A spokesman for South East Water said the record-breaking hot weather in July exacerbated what had been the driest eight months since 1976.
July only had 8% of the month's average rainfall, and the long-term forecast for August and September is for similar weather, he said.
Last week, Southern Water also announced a hosepipe ban for Hampshire and the Isle of Wight.
The ban in the South East means anything designed, adapted or used to serve the same purpose as a hosepipe cannot be used, like sprinklers and irrigation systems or pressure washers.
The water company spokesman added: "We have been producing an additional 120 million litres of water a day to supply our customers, which is the equivalent of supplying a further four towns the size of Maidstone or Eastbourne, daily.
"We have been left with no choice but to restrict the use of hosepipes and sprinklers."
The ban follows weeks of disruption to water supplies across the counties amid the heatwave, due to a number of burst pipes.
Thousands of properties on the Isle of Sheppey were without fresh water supplies for three days, while in Challock and Molash supplies were disrupted for at least five days.
David Hinton, CEO of the firm, said the dry ground conditions and the resulting earth movement had caused a 50% rise in the number of burst pipes.
Last month, South East Water's director of operations, Douglas Whitfield, said he was concerned about water levels and pleaded for customers to "really think carefully about their water use... and use water for essential use only".
However, at the time he expected water concerns to be a "short-term" issue.
