Jackson, capital city of the US state of Mississippi, is struggling to return pressure to its water system.
"We are producing significant amounts of water and pushing that into the system but the pressure is not increasing," said a statement from the city authority.
The issue has to be significant leaks in the system that have not been identified yet, Xinhua news agency quoted the statement as saying.
Officials in Jackson had issued a citywide "boil water" notice on Sunday following water line breaks due to frigid weather.
This summer, torrential rain in the Jackson area caused floodwater to seep into a water treatment plant, leading to the failure of the backup pumps upon which the facility relied.
A resulting system-wide loss of water pressure left Jackson residents, mostly African-Americans, without reliable access to safe drinking water for more than two weeks.
About 180,000 people living in the affected area were forced to rely on bottled water.
Two US congressional committees wrote a letter to Mississippi Governor Tate Reeves in October, saying that Jackson has suffered "decades of disinvestment".
"The Jackson water crisis was a disaster waiting to happen, and it will not be resolved unless we address generational disinvestment in majority-Black cities," the letter read.
The federal government has committed $600 million to help fix Jackson's water system.
The funding is included in a massive spending package which was approved by Congress before Christmas.
Last month, a judge approved a request from the Department of Justice to appoint a third-party manager for Jackson's water system.