About 31,000 properties are without water in East Sussex due to a burst water main.
Southern Water said the disruption in St Leonards-on-Sea and some areas of Hastings was expected to continue into Sunday.
The issue was first reported on Thursday afternoon and the company has opened water bottle stations and said it was delivering bottled water to more than 6,000 customers on its priority services register.
Schools, a leisure centre and a theatre in the area have been forced to close.
Southern Water said in an update on Saturday morning: “Our teams worked through the night to remove the broken pipe and replace it with a new length of pipework.
“We are making good progress on the repair.
“When the repair work is completed, we will then recharge the network and restart our water supply works.
“However, this will take time and we expect disruption to continue over the weekend.”
The company added that the burst main is located in Keeper’s Wood, “deep in woodland”, which is making it difficult for crews and machinery to reach it.
Spokesperson Tim McMahon told BBC Radio 4’s Today programme: “This burst is in a very, very difficult location, I’ve been in industry for 20 years, it is by far the most difficult location I’ve ever seen.
“You know, we’ve had to fell 50 trees just to get to the burst.”
Lesley Arshad who lives in St Leonards-on-Sea and is disabled told the Today programme she had been left off the priority list by the water company.
Arshad said she contacted the company to be put on the priority list last year and was sent a letter confirming it, yet when she rang on Thursday to ask for water she was told she was not on the priority list.
She said: “I rang the customer service representative and he said that I wasn’t on the list and I said that I had received a letter from Southern Water to say that I was.
“He said: ‘Oh it’s probably because you live in a flat.’ But he said I would get some water but [he] not sure when I would get it.”
A spokesperson for Southern Water said the firm had been in touch with Arshad and would deliver water to her on Saturday.
They added: “We’re supplying more than 6,000 vulnerable customers who are on our priority service register in the affected area, and will investigate any issues where people who are on our list to receive water haven’t.”
Peter Haldane, 43, of the Highlands Inn Hotel & Bar, told the Telegraph he had to queue for three hours to collect 30 bottles of water.
He said there was no running water at the hotel, which expects to lose thousands of pounds in revenue.
“We had 10 rooms fully booked and we’re expecting that nine will cancel.
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“That’s £100 a night.
“They are well within their rights to cancel.
“We don’t have working toilets or showers.”
This weekend is the four-day Jack in the Green festival in Hastings, which Haldane described as “one of the biggest weekends of the year”.
Bottled water stations have been set up at Asda and Tesco in St Leonards-on-Sea and Sea Road in Hastings.
The White Rock Theatre was closed on Friday due to the water supply issue.
The theatre cancelled its Millie’s Nightclub event, a pop-up nightclub for adults with learning disabilities, which was due to take place on Friday, and a Saturday performance by Brown Boots Boogie Band.
It posted on its website saying it was “deeply disappointing” that the issue coincided with the area’s annual Jack in the Green celebrations.
Summerfields Leisure Centre posted a statement on Facebook on Friday afternoon: “Due to Southern Waters disrupted supply the centre is currently without any running water and therefore cannot open until the supply resumes.
“As this problem does not seem to have a quick fix we have made the decision to close the centre for the rest of the day and will update tomorrow when we know more.”
A notice on Churchwood Primary Academy’s website says it is closed as there is no water supply in the area.
St Paul’s Church of England Academy in St Leonards was closed on Friday.
