Detour signs were put up on Monday, Tuesday and Wednesday while workers from Killard Infrastructure dug down to the old cast iron pipes, removed them, and replaced them with "blue brutes" - the curious name for new light-blue 150mm PVC pipes.

In his quiet Irish brogue, Killard foreman Brian Traynor explained there were four connection points, and the contractors took them in stages so they could keep the traffic flowing, at least partially.

"It was either that or try and do it in two days, but you'd be talking about closing the whole roundabout if you did that," he said.

"The old iron pipes in the main street were concrete-lined, and in pretty good shape. The new pipes will have a much longer life expectancy."

Killard's work on Coota's water mains, funded by council using a $2 million State government grant, aims to accelerate the council's program to eventually renew all the pipes in the town's 70-80km network.

The project started in September 2018 and it's estimated around 25km of pipes will have been replaced when it finishes around March or April.

Mr Traynor said there had been some areas where the pipes were better than expected, so the council had subtracted these, but added other areas where the pipes were in bad shape.

"At the minute we're doing Pinkerton Road from Carool to Parker - that just started before Christmas, and we're down to Bradman - and there's also Yass Road, which will involve some boring under the railway line."