So basically instead of using air or dirt as the medium to exchange heat from when using heat pumps it's using the water going down the drain (well it's using that and some amount of dirt because cold NYC days would probably still overwhelm it). Even if that water is tepid that's pretty smart, you aren't holding a bunch of sewage, mostly just running tepid /warm water over some very cold pipes so they can pull more heat out.

If you are unsure what heat pumps are and why they are big part of our future: https://www.youtube.com/watch?v=7J52mDjZzto