The joint venture, comprising Bouygues Construction and Robb Carr, recently launched TBM Jane Starkey to build a tunnel approximately 1.2km long.
Another160m of the pipeline will be trenched.
The new pipeline for Sydney Water is starts at Thornleigh Reservoir and will be excavated to the south side of Zig-Zag Creek at the Thornleigh-Wahroonga Water Pumping Station. Construction is expected to be completed in 2027.
The 180cm diameter pipeline will run parallel to the existing one. It will go under private properties and cross local roads, between 14-38m underground.
The project aims to increase the resilience of the local drinking water supply and cater for the expected housing growth in the area.
The TBM is named after Thornleigh nurse Jane Starkey who was known for her welfare work with women and children in the early 1900s.
Last month tunnelling commenced on the North West Wastewater Connection, another Sydney Water project.
