A temporary road closure has been put in place for the B4350 Castle Street in Hay-on-Wye.
Welsh Water will be carrying out work on the street to renew the water mains.
The work will take place from Monday, October 16 until Tuesday, October 31.
Powys Highways have said no vehicles or pedestrians should proceed onto Castle Street from the junction of the B4350 Church Street to the junction of the U0771 Castle Street for a distance of 60 metres.
Residents access and emergency vehicles access will be maintained via diversion.
Alternative routes will be signposted.