More than 300 homes in West Sussex have been left without water for five days as temperatures hit 35C.
The households have not had running water since Friday due to low pressure caused by more people and businesses running their taps.
Specialist water tankers have had to be brought in, along with bottled water stations to help the desperate residents.
South East Water said the shortage is due to the extreme demand in water as temperatures soar during Britain's hottest heatwave on record.
The water company said more people taking “staycations” was "putting a strain" on the country’s water network.
Last Friday, regional water usage hit a record for demand of 696 million litres, South East Water said.
But residents argued the water company should have been more prepared for the crisis.
Neil Davies, who lives in the village of Warninglid, said: “It is a ridiculous situation.”
Nigel Gordon-Stewart, also of Warninglid, described the situation as “deplorable”.
He added: “It is 34C and we can’t shower, flush our toilets, wash our clothes.
“It takes about four or five bottles to flush the toilet.
“We can’t live like normal human beings, and we have to queue in the heat for bottles of water that are wrapped in plastic, which completely goes against climate change.”
The villages of Bolney, Bolnore Village, Cuckfield, Haywards Heath, Slaugham and Warninglid were all affected by the outage, with others in the area also suffering from "intermittent supplies".
The nearby Warninglid Water Tower and Cuckfield underground storage reservoir became low over the weekend, meaning water pumps were unable to boost supplies as normal, South East Water said.
Some households in West Sussex had their water supply restored overnight.
South East Water said it supplied 673 million litres of water on Tuesday, which is around an extra 130 million litres.
The firm issued a warning to customers on Saturday that they could be without tap water unless its usage is cut this weekend.
But Gordon-Stewart, 59, who currently lives with his daughter, 29, said the warning came too late.
The business consultant said: “South East Water was not prepared for this.”
Steve Andrews, head of central operations at South East Water, apologised on Tuesday for the problems and pledged to restore the service.
He added: “We are very sorry and can only reiterate that we are doing everything we can and are working 24/7 to meet the demands for water – please help us by avoiding all garden water use this week.
“Storms are forecast and cooler weather is on its way.”