Just outside my office window is a heat pump, which provides our house with low carbon heating and hot water. It’s an air source heat pump, which means it draws heat from the air and channels it into the house. There are other forms of heat pumps, notably ground source, and less well known is the water source heat pump. I’ve written before about a scheme to use London’s underground rivers as a heat source, but it remains a fairly unusual technology.

As the name suggests, water source heat pu...