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, but most of it is being lost in leakages from burst pipes. About 32,000 properties are affected 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 Friday afternoon. "It could be early next week before everybody is on supply," he said.
The ministerial Executive is to hold an emergency meeting about the situation.
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."