In its interim financial report, the company said it had produced 127GWh of energy from sludge in the first six months of the year.
By not having to import this energy from the grid, Thames saved £15 million on its energy bill, and this is set to increase as the firm maximises the benefits of new technology.
The company has also increased its solar energy output, having produced more than 7,200 MWh of power from panels on its sites, including the floating solar panel array on its Queen Elizabeth II reservoir, during the last six months.
Thames has set itself a target to produce 33 per cent of its own energy from renewables by 2020.
The group said it had invested £540.9 million, as part of its £4 billion AMP6 (2015-20) investment programme.
Underlying profit before tax was down at £127.3 million, compared with £216.8 million the previous year, excluding impact of net losses and gains on financial instruments.
Thames also revealed that Castle Water paid £99 million for its business customer base. The company announced its decision to exit the market in July this year.
As the UK’s largest water and wastewater service provider, Thames serves 15 million customers across London, the Thames Valley and surrounding areas. It provides 2.6 billion litres of clean drinking water and removes 4.4 billion litres of wastewater every day.