The city closed the 1800 block of Martin King Luther Jr. Boulevard on Tuesday morning to repair a broken main.
That is the section between Peyton Street and Grantland Drive.
Posted detours take eastbound drivers south of the closed section. Westbound drivers are being directed on a route that goes north of the work area.
The city said it expects the work to be finished by noon.
Municipalities around the Triangle have been plagued with water-main repairs since unusually cold weather began.