Water has been lost to further homes in Sussex, where more than 300 householders have been without supplies since Friday.
South East Water said some customers in East Sussex had low pressure or no water due to a burst pipe.
It said, however, that supplies had been restored overnight to the areas of West Sussex which had been without water for five days.
Bottled water stations have been set up by the company.
The latest problems are hitting customers in Rotherfield, Crowborough, Mayfield, Hadlow Down and Five Ashes, as well as some in Heathfield.
Gary Walker, from Warninglid, said he had been forced to “manually remove waste from the toilet and bury it in the garden”.
Di Holwood from Bolnore near Haywards Heath said it had been “horrendous” living without water since Friday, but her supply had returned about 02:00 BST.
“I have no confidence this water is going to stay on for more than a few hours.”
Customers in Haywards Heath, Cuckfield, Warninglid, Slaugham and Bolney in West Sussex have seen water supplies return overnight.
Steve Andrews, head of central operations for South East Water, apologised and said: “Supplies have been restored overnight and we are more hopeful we will be able to maintain those supplies throughout the day.
“We are continuing to ask customers to only use water for essential use.”
He said more than 150 million litres of extra water was being pumped into the network as the UK heatwave continues.