Dwr Cymru Welsh Water has begun work on a £1.5m investment scheme to upgrade the sewerage network at Kilgetty.
The scheme to refurbish 4km of pipeline will improve the local sewerage network as well as bringing environmental benefits to the area.
It is taking place in Carmarthen Road, where temporary traffic lights will be in operation for 14 weeks. Other areas affected by the work include Begelly Cross roundabout and New Road.
Dwr Cymru Welsh Water investment manager Martin Kilroy said: "This is an essential scheme to upgrade the sewer system for the residents of Kilgetty and will have a long term environmental impact in the area. We apologise for any inconvenience the work will cause, but would ask people to bear with us whilst this vital work is carried out."
The work, due for completion in September, is being carried out by Meica Process, Morrison Construction and E. C. Harris, members of the Welsh Water Capital Alliance. The alliance is a strategic partnering team, made up mainly of specialist engineering and construction companies, formed to deliver around 60 per cent of Dwr Cymru Welsh Water's capital investment programme from 2000 to 2005.