Scotland´s sewers contain enough heat to warm a city the size of Glasgow for more than four months a year, according to a renewable energy group.
Scottish Renewables found 921 million litres of waste water and sewage were flushed down toilets and plugholes in Scotland every day.
It said water in UK sewers can be as warm as 21C (69.8F).
The group claimed heat pumps and waste water recovery systems could harness that energy potential.
It added that capturing warmth contained in discarded water could prevent more than 10,000 tonnes of harmful CO2 entering the atmosphere every year.
The statistics were produced for the renewables group by Scottish Water subsidiary Scottish Water Horizons.
Stephanie Clark, policy manager at Scottish Renewables, said: "These new figures show the enormous scale of the energy we are literally flushing away every day.
"Water which is used in homes and businesses collects heat from the air around it, as in a toilet cistern, or is heated, as in dishwashers and showers.
"That´s in addition to the energy that it gains from the sun when stored in reservoirs.
"Technology now exists which allows us to capture that energy and waste heat can play an important role in helping us reach our challenging climate-change targets."
´Sustainable heating solution´
Donald MacBrayne, from Scottish Water Horizons, said he believed heat in waste water was a valuable commodity.
He said: "Water that is flushed down the drain from homes and businesses represents a significant source of thermal energy.
"Usually, this heat is lost during the treatment process and when treated effluent is returned to the environment.
"By tapping into this resource using heat recovery technology we can provide a sustainable heating solution which brings both cost, carbon and wider environmental benefits.
"With almost 32,000 miles of sewers pipes across Scotland and more than 900 million litres of waste water treated every day, the opportunities presented by heat recovery are significant."