Anglian Water has restored supplies to “many customers” but people in four areas are without water for a second night, the company said.
In a statement posted on Twitter, Anglian Water said “air trapped in the pipes means that some customers in Leighton Linslade, Pottsgrove, Milton Bryan and Southcott are still without water”.
It added: “We are working hard to fix this, and we will continue through the night until it is resolved.”
Earlier, the company was branded “disgraceful” by residents after thousands were left without water.
The supplier had initially said the problem which began on Friday evening in the area of Leighton Linslade, Bedfordshire, home to an estimated 40,000 people, would be fixed by midday on Saturday.
At 3pm it said water “should be coming back on now” for all except those in northern parts of Leighton Buzzard – for whom “the delay might be slightly longer”.
But by 4.30pm, many residents continued to complain supplies had not returned, even in the south of the area, and some were unhappy with Anglian Water’s communication.
The company said the initial problem was caused by a damaged valve. Issues began with water running yellow and cloudy at around 6pm on Friday before supply stopped entirely.
Resident Richard Ayre told the PA: “The main concern is that they are saying it is one valve that has caused the issue.
“Surely the town and the villages are not all supplied through one pipe.”
Anglian Water said bottled water is available for affected customers from Tesco on Vimy Road and Brooklands Social Club on Garden Leys – or for delivery by calling 0800 145 145 for those on Anglian Water’s WaterCare register.
Mr Ayre, 29, said he had not been made aware beforehand of the register.
“Otherwise we would have signed up as a relative has just been released from hospital and needs to take in a large amount of fluids,” he said.
Complaints about the water supply issue were so widespread that Leighton Buzzard was trending on Twitter on Saturday.
Anglian Water added: “We would like to thank customers for their patience while we carry out this work.
“We are genuinely sorry for the disruption this has caused, rest assured our teams will continue working to get things back to normal as quickly as possible.”