Hundreds of homes in southern England were left without running water for days after the heatwave triggered extreme demand.
About 300 households in mid-Sussex have not had water since Friday when temperatures reached 35C, while others had intermittent supplies and low pressure.
South East Water said demand in the area on Friday was a “record” 696 million litres – over 150 million litres more than typical supply.
The coronavirus lockdown and staycations are also playing a part in the surge in demand, utility suppliers said.
Water bottle stations have been set up, and about 32,000 bottles delivered to vulnerable people, while 23 bowsers were deployed to help deliver to homes and businesses with livestock.
South East Water said it is working 24/7 to try to restore supplies.
The supplier added: “We will continue to operate tankers in the area trying to inject water into the network, but it is very complex and will mean supplies continue to be intermittent.”
A further 4,400 homes in East Sussex had supply issues for several hours on Wednesday after two water mains burst.
Repair work was completed and taps started running for most homes in the area overnight, but some residents in Crowborough and Jarvis Brook still had no water on Thursday.
Steve Andrews, the head of central operations at South East Water, said: “We are working to remove airlocks in our extensive and complex pipeline network in the area and investigating a report of a further burst water main in the area.”
Other water companies in the south of England issued warnings to customers about extreme demand and urged them to limit consumption to essential use or risk losing supply.
Bob Taylor, the chief executive of Portsmouth Water, said demand hit a 10-year high over the weekend – almost 70 million litres above the daily average.
He added: “We are asking customers to restrict their use of water during the next few days of the heatwave to ensure that all customers receive a reliable water supply.”
Southern Water, meanwhile, deployed tankers in the Buchan Hill area in Sussex to redistribute water to support what it described as “unprecedented” demand.
A spokesperson from the supplier said it is not a water shortage issue they are experiencing, but a supply and demand issue.
They added: “People are using it quicker than we can treat it and pump it through to people’s houses.
“The reservoirs are looking good but you can’t drink raw water, it’s a product and there is only so much we can treat at a time.”
A Water UK spokesperson said: “The unprecedented combination of record-breaking temperatures and lockdown, resulting in more people staying at home or holidaying in the UK, has meant huge demand for water, especially in south and southeast England.
“This demand has put exceptional pressure on supply, with companies working flat out to produce water fast enough to match the speed it’s being used in homes and gardens.
“Water’s a precious resource and we want everyone to have what they need, so our Water’s Worth Saving Campaign has been encouraging everyone to think about the water they use, and offering simple water-saving tips, as even small changes can make a big difference.
“One example is the paddling pool in the back garden – great fun, but it uses the same amount of water as a family of four consume in a day so best to re-use it and not re-fill it every day.”
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