The deals on what is the industry’s longest alliance deal will be worth more than £200m over the next 15 years.
The four firms were first named preferred bidders late last year and will be responsible for Anglian’s water recycling infrastructure maintenance work – around 7,500 jobs every year.
These include fixing collapsed sewers and replacing damaged manholes.
A total of five firms will be used in the IMR alliance, one of four alliances that Anglian Water has now established to deliver its business plan for AMP6 and beyond.
The IMR alliance is divided into two specialist areas, covering water and water recycling work.
The latest four contractors join Clancy Docwra and Kier MG, which signed contracts last November to carry out the water supply maintenance programme.
Partners on both parts of the IMR alliance will be encouraged to contribute ideas and experience across both areas of work.
Supply chain contracts begin in April and are expected to run until 2030, with a review every five years.
Jason Tucker, head of supply chain management for Anglian Water, said: “The signing of the IMR alliance completes the four tier one framework alliances, which will deliver Anglian Water’s business plan for AMP6 and beyond.”
“We now look forward to running additional procurement processes to appoint our many tier two partners to service our four alliances.”
Jim Davey, Associate Director of Clancy Docwra, added: “We are confident that our collaboration with our fellow partners will successfully deliver the Anglian Water business plan and outcomes and ensure that we continue to drive efficiency and innovation to deliver a first class service to Anglian Water and their customers.”