NI Water have said it could be next week before all homes and businesses in Northern Ireland are reconnected.
Ministers in NI are to hold an emergency meeting to discuss how to help the 36,000 people still affected as it emerged that two hospitals have experienced supply problems.
South Tyrone Hospital in Dungannon has been relying on the NI Fire Service and bottled water.
Lagan Valley Hospital in Lisburn was without water for a number of "hours".
Eighty villages and towns have been affected as pipes burst in the thaw.
The Stormont Executive will discuss what further measures can be taken.
Deputy First Minister Martin McGuinness has said he feels "absolutely let down" by NI Water's response.
The state-owned company, which is the sole provider of water and sewerage services in Northern Ireland, said an unprecedented number of leaks caused by the thaw following the long period of freezing weather had been putting "big pressure" on its systems.
Mr McGuinness said people had not been given enough information as to when water would be restored.
"My focus is on how NI Water can do things better over the course of the next number of days," he said.
The thaw followed the worst snow in Northern Ireland in 25 years and record cold temperatures.
As temperatures rose, burst pipes drained reservoirs, forcing NI Water to turn off the tap to the 80 locations.
Some people have been without water for 11 days.
BBC Northern Ireland's political editor Mark Devenport said there was recognition that NI Water's engineers were struggling to deal with an unprecedented number of call-outs, but there was also general condemnation of the company's inability to communicate better with its increasingly angry consumers.
The Stormont Executive has accepted help from Scotland and sent civil service staff to help out at NI Water's call centre.
Ministers will want to discuss at Stormont what further measures can be taken to resolve an emergency which has raised fresh questions about historic under-investment in Northern Ireland's outdated water network, our editor adds.
'Crisis wasn't made by politicians'
Minister for Employment and Learning Danny Kennedy is attending the meeting.
"I believe that this crisis wasn't made by politicians," he said.
"I think it does prove to me that there was inaction and ineptitude on behalf of senior executives in NI Water who failed to recognise and prepare properly between the period of the big freeze and the big thaw so they bear heavily responsibility.
"Now if they are able to transform radically the situation then it may well be that they will save their skins but I think the public are looking for answers and there must be an immediate response from not only the Executive but also NI Water itself."
The interim chairman of NI Water, Padraic White, admitted its response had been unsatisfactory.
"The organisation has to improve its performance, has to improve its communication and, I believe, will improve its communication over the next two days or so," he said.
"I empathise as interim chairman with those people who haven't had water for the last two or three days - that's an awful situation to be in."
Northern Ireland Secretary Owen Paterson said that while the Westminster government had a lot of pressures on its budget, it was also ready to help.
He said Northern Ireland's infrastructure had suffered over the years and that changes were now needed.
"What will be looked at here is the difference in the way that water is paid for in the rest of the UK and the way it is paid for in Northern Ireland, where it is just an element of the rates," he said.
"I think what is clear is that the events of the last week or so will bring this to a head. It is a major issue that has to be resolved."
Mr Paterson said the wider infrastructure problems were for the Stormont government to address.
"This is a local responsibility now," he said.
"NI Water is an organisation responsible to local ministers and it is up to them to decide in response to their voters how they organise and how they fund water supply in Northern Ireland."
NI Water is now operating water "black outs" where householders' supplies are interrupted for a period of six to eight hours, then turned back on again.
NI Water's head of customer services Liam Mulholland said it is a "slowly improving situation".
"We'd like to see that improve much more quickly," he said.
"We're doing everything we can. It will continue, I suspect for another few days.
"We want to keep that as short as is physically possible and I do want to apologise to customers and I appreciate their patience with us."
Mr Mulholland said some people are still not aware that they have been affected.
"I'm fearful that, as many businesses return to work on Thursday, we're going to find a lot of people arriving into circumstances that no-one wants to be in, with burst pipes, broken ceilings, businesses that are going to be affected in already difficult times," he warned.
The company said it is also aware of bogus information being given to customers at their door steps concerning water supply times.
NI Water said planned times for when supplies will be switched off, for a period of time, and then restored are indicated on the major incident page on its website.
The company said all NI Water staff should have ID cards with a photo of that person, their name, a unique serial number and logo.
Local councils are working to supply water and offer free showers to people without a mains supply and information is being provided on the NI Water website.
The Scottish government is providing 160,000 litres of bottled water, the first shipments have already arrived.
More information is available from the NI Water website, or telephone hotline: 08457 440088, on Ceefax 169 and BBC News Online.