A renewable energy group has claimed that Scotland's sewerage system could be used to warm a city as big as Glasgow simply by reusing the heat found in the underground systems.

Scottish Renewables has calculated that 921 million litres of sewerage and waste water are flushed through the system each day in Scotland, and the water can be as warm as 21 C. If this was fully utilised, the group say, it could provide enough renewable energy to heat a city of Glasgow's size for over four months every year.

Scottish Renewables has suggested that waste water recovery systems and heat pumps could be deployed to make use of this trapped heat and release its energy potential.

Its research - produced for Scottish Water - also shows that if the heat energy that is trapped in the waste water could be captured, it would prevent over 10,000 tonnes of greenhouse gases from being released annually.

Scottish Renewables' policy manager, Stephanie Clark, said that the research showed that there is tremendous energy potential in the waste products that are literally flushed away into tunnels every single day.

The heat in the water is trapped from surrounding air or produced hot at source, such as in showers and dishwashers. Even toilet cisterns heat water through use. Additional warming occurs when the sun heats the water and waste products in reservoirs.

Modern technologies, she added, could now allow this heat energy to be captured and reused in order to provide district heating and prevent carbon dioxide from being released needlessly into the atmosphere from waste.

Scottish Water added that they believed waste water heat could become a valuable commodity, and that thermal energy extraction could provide a sustainable district heating solution that would cut carbon emissions and costs.