Do you know what “grey water” is? Grey water is all household wastewater that hasn’t been used in toilets. 50% -80% of any households water usage will end up as grey water. What happens next is really disappointing though. All of this reusable grey water is mixed with unusable “black water” or sewage water and sent down the sewer to the local wastewater treatment plant before it’s dumped into the nearest river or estuary as effluent.