branched water supply to city for heat-pumps

I think it would be slick if a city could be designed to take water from a river, filter it, and then supply it to all the buildings within it using a branched network of pipes.

The buildings could use water source heat-pumps to remove heat from the water, and then discharge it into a reverse branched set of pipes to be returned to the river a little colder.

This might be a fairly cheap way of providing the functionality of a ground-source heat pump.