An Edinburgh-developed home heating system uses water, the world's most abundant resource.
Using air source heat pump technology, the equipment may heat radiators and bathtubs and showers with sea, river, pond, or mine water.
Edinburgh University is testing it in an affordable housing project near the Forth Bridge, a gold-mining museum in southwest Scotland, and a commercial greenhouse in Fife.
The Scottish Seabird Centre in North Berwick will install another Firth of Forth-powered system this summer. All systems use sea or river water.
The latest method of heating buildings with ambient warmth from the natural environment uses air and ground source heat pumps.
Glycol, used in anti-freeze, is squeezed in the heat pump to capture sea or river water heat.
. Compression heats water for radiators or baths. The liquid cools again in the heat pump, repeating the process.
The Queen's Quay housing estate in Clydebank, Glasgow, uses Clyde water for district heating.