The contract, which runs until April 2020, has the option to be extended for a further five years.
Starting from 26th September, Amey will repair and maintain 20,000 miles of sewer pipe connecting nearly two million homes to more than 600 waste water treatment works in the area.
The Spanish-owned contractor has already worked for Yorkshire Water for five years. The new services Amey will be providing are in addition to its current framework for non-infrastructure projects in the region.
Amey chief executive Mel Ewell said: “The awarding of this contract to Amey is testament to the strength of our relationship with Yorkshire Water and their trust in our ability to deliver services to the highest possible standards as well as our considerable experience in the waste water industry. We are delighted to expand the scope of our work with Yorkshire Water. Both our organisations will work together to improve essential services and provide an outstanding customer experience across the region."