The most common heat pumps in the UK are either ground source or air source. However, water can be used as well as another source of energy for heat pumps. Most efficiently water source heat pumps are used to provide heating in homes near to rivers or lakes.
Moreover, water as an energy source can help you reduce the cost of installation, because there won’t be any need of digging large trenches. Another fact is that the return temperature to the heat pump is much higher compared to ground or air, which increases the performance of the heat pump. And don’t forget the heat transfer rate from water is much higher that that in the ground or air.