It could be early next week before all Northern Ireland customers cut off from water supplies are reconnected.
Around an extra 250 megalitres are being pumped into the system every day, Northern Ireland Water said today, but most of it is being lost in leakages from burst pipes.
About 32,000 properties will be affected today but the situation is improving in Belfast.
Trevor Haslett, director of engineering at NIW, said the situation in urban areas was improving and should be better by tomorrow afternoon.
"It could be early next week before everybody is on supply," he said.
The ministerial Executive is holding an emergency meeting today. The Scottish Government has donated bottled water and the Westminster coalition says it is ready to help.
NIW believes much of the leak is coming from vacant business premises.
One property in the north of the region was gushing out enough water to cover 2,000-3,000 houses.
An extra 40% of water is being put in every day to support dwindling reservoirs but much of this is disappearing in leakages.
Temperatures in Northern Ireland hit a pre-Christmas record of minus 18C and were followed by a dramatic thaw, causing thousands of burst pipes.
Laurence Mackenzie, chief executive of NIW, is facing calls from political rivals of Sinn Fein water minister Conor Murphy to resign.
"My focus at the minute is getting through this situation," he said. "I have been in here since the issue arose. I believe I am doing the best I can to keep the team together and keep focused."
Mr Haslett said over a period of 12 hours the company suffered more burst service pipes than he could remember for 35 years.
They have invested £150 million in water mains over the past three years, replacing 1% of their system but in other parts of the UK almost double the amount of infrastructure had been replaced.
"If NIW received more money for water mains we could increase the rate of renewal," Mr Haslett said.
Even before this month's bad weather, almost a quarter of water was lost in leakage.
Engineers have discovered a property in the north where enough water has been lost to cover 2-3,000 homes and officials asked the public to check their premises.