More than 100 metres of new pipes have been laid through Mill Street already this year after flooding last year pushed the work up the priority list.
Guernsey Water said some of the pipes it is currently replacing are 80 years old and burst twice last year. One business was flooded as a result.
The work started on 2 January but has been hampered by the almost constant rainfall experienced so far this year with Guernsey getting nearly 80% more rain so far in 2026 than average.
Despite that, Guernsey Water said its crews have been replacing around 10 metres of the main each week.
That work involves digging down to the original cast iron pipe, isolating and removing the old section, installing a more durable plastic main, scrubbing and relaying each individual paving stone before reopening the area to pedestrians.
Local contractors are doing the work, and Guernsey Water’s Capital Delivery Manager Carl Falla said this will ensure skills and investment remain within the local economy while also future-proofing the Old Quarter’s water supply for a long time to come.
“This is a major piece of work that will future-proof the main in that area until nearly the turn of the next century,” he explained. “We know this is disruptive work, and that’s why we chose January to start the work to allow the Christmas trading season to happen for the local businesses.
“We hand delivered letters to all of them and have kept access to businesses open throughout.”
This project is part of a broader 2026 plan where Guernsey Water expects to invest in both the water and wastewater networks, with the company planning to invest nearly £130 million by 2037.
“Doing nothing is not a cost-free option and simply stores up problems for the future,” said Mr Falla.
“This is one project of many investing in critical infrastructure during 2026, when in total we expect to spend £7.8m. on maintaining and upgrading the island’s water and wastewater networks.”