Thames Water is seeking contractors for up to £900M of AMP6 work.
The utility giant advertised in OJEU for firms to form its alliance to deliver capital works through the five-year asset management period beginning next spring.
Work will range from water network repair to district metering, and include planning and project management.
If successful, the agreement could be extended for a further decade and potentially be worth well over £2bn.
Contractors have until 16 July to register their interest in the framework.