Under the five-year contract, Haven Power and a part of Drax Group will supply clean electricity to allow Thames Water provide water and wastewater services to its customers.
Thames Water energy manager Angus Berry said: "This deal with Haven puts downward pressure on bills and means we will now be using 100% renewable electricity.
"We look forward to growing our relationship with Haven to exploit further opportunities to minimize energy costs and emissions, as well as continuing to work towards our ambitious target of self-generating 30% of our own electricity by 2020."
Haven will also oversee demand management and metering and data provisions.
Haven Power CEO Peter Bennell said: "From SMEs right up to large commercial and industrial businesses, our Renewable Power option is an excellent way for companies to improve their sustainability credentials – and it doesn’t cost the earth."
The deal has an option for two further five-year renewals, which will bring the contract value to more than £1.5bn over 15 years.
Thames Water currently sources 20% of its electricity needs through renewables, including solar, wind, hydro and biogas.
Drax supplies electricity to Haven Power from its 4GW plant inYorkshire, UK.
The power facility, which serves around 8% of the UK’s power requirements, is being converted from coal to biomass.
Image: Thames Water and Drax officials. Photo: courtesy of Haven Power.
