Five water suppliers in England and Wales are being allowed to increase their bills after being given the provisional go-ahead for extra spending.
Regulator Ofwat says the money will go towards improving infrastructure and addressing rising demand caused by housebuilding.
Debt-ridden Thames Water, Severn Trent, Southern, Wessex and South East Water could all potentially put up costs between next year and 2030.
Thames Water is currently imposing a hose-pipe ban.
Meanwhile, SES Water, which covers parts of Surrey and London, is asking its customers to help reduce water use as prolonged hot, dry weather continues “to drive exceptionally high demand across the area.”
Bosses say the sustained heatwave has put pressure on parts of the drinking water network as demand across the region has increased by around 40 million litres per day.
Last week, the Environment Agency declared half of England, including the SES Water supply area, in drought, with more of the country included earlier this week.
More recently, the Met Office has warned of a further notable heatwave developing over the coming days, following on from provisionally the second warmest July on record for the UK.
To help maintain supplies for customers, SES Water is asking customers and visitors to the area to use water with care until temperatures start to fall.
Daniel Kennedy, Director of Water Services at SES Water, said: “The prolonged hot weather over the last few weeks has resulted in exceptionally high demand on our drinking water network, and while we do not have a hosepipe ban in our area, we can all play our part in reducing the water we use.
Our teams are working around the clock to move water around the area, bring in supplies from areas under less pressure, and maximise production at our treatment works.
To help protect water supplies across the network and reduce the risk of supply interruptions, we are asking customers to reduce their water usage where possible until temperatures begin to drop.”
