The Southampton link main (SLM), is expected to cost more than £100m to complete over the next three years, and will link the Otterbourne water works with the city of Southampton.
It is being put in to reduce the impact of any burst pipes, mechanical failures or leaps in demand in the future, by making it easier for Southern Water to move water around the network to where it is needed most.
The pipeline will link up with two underground reservoirs – in Yew Hill to the north where a new storage tank is also being built, and at a site on the outskirts of Southampton. This will allow Southern Water to build up reserves and, in turn, reduce the amount of water that it takes from the Test and Itchen chalk streams.
The works are being delivered by MGjv, a joint venture between M Group Water and Galliford Try.

Southern Water programme manager Simon Cook said: “It’s great to get this project under way. We’ve worked closely with landowners and local authorities to find the most viable and least disruptive route for the pipeline.
“We are doing this to improve the resilience of our water network for our customers in Hampshire. The project will also provide future resilience for the Test and Itchen rivers and their wildlife.â€
Most of the pipeline will be laid by digging trenches, installing the pipeline and then backfilling with earth. However, in some areas, it will be installed by digging tunnels deeper underground to avoid disruption to major roads, railway lines or ecological sites.
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