The four-year deal is for monitoring and maintenance work on the Thames Water Ring Main and Raw Water tunnels.
Barhale will be responsible for 35km of ring main tunnels and a further 9km of raw water tunnels.
Associated works include the refurbishment of four High Integrity Valves and relining a 1.8km length of the 2.5m inlet and outlet tunnels for the QEII Reservoir at Walton-on-Thames.
Phil Cull, Barhale’s Southern Region Director said: “Under AMP6 we worked closely with the Thames Water team to refurbish 19 of the 22 shafts.
“It’s meant that we have gained insights and knowledge of working across the Ring Main that is second-to-none.
“We are very pleased that experience has been recognised by Thames Water and to be given the go-ahead on this important programme of works.”
Mark Grimshaw, Water Production Manager for Thames Water, said: “Providing a reliable and safe supply of water to our customers is a top priority for us so it’s vital we have the right people working with us to look after the infrastructure that makes it possible.
“We’re glad to once again have Barhale on board to maintain and improve such key pieces of our London network.”