Clean water flowing in the pipes to a house will often be warmer than outside air during winter and have a higher heat capacity than air used in heat pumps.
No idea if using another heat pump and lowering the temperature from say 10C (ignoring any water heating in the house) to 6C of the gray water flowing out of the house makes sense.
No idea if using another heat pump and lowering the temperature from say 10C (ignoring any water heating in the house) to 6C of the gray water flowing out of the house makes sense.