Work will start shortly to upgrade the Acomb Landing water treatment works in York and the Caldervale waste water treatment works in Wakefield at a combined value of £25m.
The projects are the first schemes to come through under the £330m Yorkshire Water Large Schemes framework.
Galliford Try and Aecom are one of four framework contractors who will carry out major upgrades to water and waste water treatment works as well as schemes to improve the quality of bathing water on the east coast of Yorkshire.
Greg Fitzgerald, Chief Executive of Galliford Try plc, said: “We are delighted to be able to continue our longstanding relationship with Yorkshire Water with a service for their Large Schemes framework.”