Scottish Water is using a water service reservoir with treated water located in the heart of Oxgangs area of Edinburgh supplying drinking water to generate electricity as a by-product.

Edinburgh is home to the country’s only treated water hydroelectricity site located within a major town or city - hydro-electricity usually happens out in remote hills far from urban areas.

The site, powered by treated drinking water, generates enough energy to supply the National Grid. Local power consumers include dozens of houses, a large care home and a major secondary school in the Scottish capital.

Scottish Water’s Firrhill Service Reservoir holds a colossal 18,200,000 litres (18.2 ML) of fresh drinking water.

The site in Edinburgh has been in place for 65 years – but for the last four years it has harnessed modern day energy technology to provide all of the site’s electricity. It works so efficiently it also feeds around 60 000 kWh of electricity per month to the grid.

Claire Chapman, Renewable Generation Manager at Scottish Water, said:

“Firrhill is a hidden gem in terms of renewable energy. And I am sure very few people know it is there let alone what it does. There is no noise and the site just looks like an empty field, as the water is all stored underground. It is also unusual to have treated drinking water used to generate energy – there are only a handful of places in Scotland where this happens.”

Energy is harnessed from the flow and pressure of water arriving at the site, powered through the hydroturbine inside a small powerhouse at Firrhill. A 160 kW Turbo Impulse turbine Machine, sits next to a generator at the site and harnesses the pressure and converts this to energy.

The clean drinking water flows by gravity from Glencorse Water Treatment Works located in near Penicuik – which in turn is supplied by gravity from Megget reservoir in the Borders. It comes into the site at a speed of 222 litres a second – and because no pumping is required throughout its journey, which generates energy en route, the drinking water in Fairmilehead has a particularly good carbon footprint.

Firrhill reservoir supplies approximately 38,000 homes with drinking water. At the same time, it is generating around 60000 kWh/month of energy every month – this is enough to power 228 average sized homes every year.

Claire Chapman added: “The excess electricity it makes is used in the area, meaning there are no line losses from the power being transported to other area – losses which can amount to as much as 50 per cent. Like water, electricity moves where there is demand – and there is plenty of demand right here in the city next to the Firhill site.”