Abstract: A grey water heat recovery apparatus has first and second passes arranged in counter-flow orientation. The heat recovery apparatus is made from commonly available materials. The heat recovery apparatus has a hot side for grey water, and a cold side for fresh water supplied under pressure. The heat recovery apparatus is used to pre-heat water for a water heater, and extracts heat from the grey water drains of a building in which the grey water drains are segregated from the sewage drains. The fresh water is carried in copper or stainless steel coils or linear tubing modules in series, each coil or linear tubing module being immersed in a grey water sump in a cylindrical plastic pipe. The water level in the sump is determined by the drain outlet level, and is high enough to immerse at least the dominant portion of the fresh water coil in grey water.