A sewage works in Leicestershire is using its raw material to help power the facility.
The methane gas from millions of litres of sewage at Wanlip has begun to be converted into electricity.
Severn Trent said since it is buying less power from the National Grid the move could eventually result in cheaper bills for customers.
The method is already used at Severn Trent's works in Loughborough, Hinckley and Melton.
Wanlip sewage works processes about 185 million litres (40,700,000 gallons)of sewage every day, from more than 600,000 people.