The five-year contract, worth £129m will see Amey delivering metering installations and planned and reactive maintenance for Affinity Water.
Affinity Water operates as a water-only supply company in much of the home counties area.
Amey has worked with Affinity Water for the last 10 years providing a range of clean water services including mains renewal, new supply connections to the network, mains cleaning schemes as well as installing around 70km of new water mains every year.
It is also the sole contractor for Affinity Water in providing connections to new residential and commercial developments in their network.