THE vital statistics of wastewater are not something we would habitually contemplate. But consider these in their sanitary glory: the average modern toilet flush is six litres; 921 million litres of wastewater and sewage are flushed down Scots plugholes and toilets daily; almost 32,000 miles of sewerage pipes transmits this waste to 1,800 treatment facilities.

So much for The Effluent Society. However, shining a light down our sewers reveals other statistics that could generate more heat: the water in our sewers can be as warm as 21C; harnessing that heat could prevent 10,000 tonnes of harmful CO2 entering the atmosphere every year; indeed, it could warm a city the size of Glasgow for four months.

And that would help in meeting the Scottish Government’s draft energy strategy of generating 50 per cent of all energy from renewable sources by 2030. Scottish Renewables, which commissioned the statistics, believes the “enormous” amount of energy in wastewater could be harnessed by heat pumps.

Already, it is involved with wastewater heat recovery projects in Kirkwall, Campbeltown, Clydebank, Stirling and Glasgow, the last at Kelvingrove Museum, near the statue of Lord Kelvin, who devised the theory of heat pumps in 1852.

We like to think of him nodding stony approval from his plinth, advising: “Waste not want not.”