A major upgrade of Colac's main water supply pipeline is at the halfway mark.
About 3 kilometres of pipe have been replaced, with a further 3.2 kilometres remaining.
Barwon Water General Manager Capital Projects Paul Northey said work on the $14.7 million project had been progressing well.
"The sections that have been completed were located in the most difficult areas for terrain and access," Mr Northey said.
"It is a challenging location with steep inclines and environmentally sensitive areas so Barwon Water has used smart construction techniques, such as boring, to minimise disturbance to vegetation and fauna."
He said major work was expected to be completed in August, with some minor works to be undertaken during the drier summer months.
The upgrade will increase capacity and ensure supply security.
Bypass stations have been installed to ensure there is no interruption to Colac's supply during construction.
The 28-kilometre pipeline, which connects the West Gellibrand and Olangolah reservoirs to Colac, was constructed in 1910.
The upgrade is part of a staged replacement plan, with the first sections of the program completed between 2002 and 2007.