Grey water is the previously used water drained from sinks, showers, dishwashers and any other appliances or fixtures other than toilets.  The key distinction from wastewater is that it does not include water from any sewage streams.  Grey water accounts for 50-80% of used water that leaves the household.  In most homes, it is handled the same as wastewater and enters the sanitary sewer where it is combined with raw sewage and conveyed to treatment plants.  Instead of treating this gently used water as sewage, grey water reuse systems treat the water onsite, rendering it suitable for various non-potable uses.  The water is collected in a tank – where many solids will settle to the bottom - and then pumped off the top and through some form of treatment, which varies according to the complexity of the system.  Treatment will often include filters (e.g. screen, biological) and may even include a disinfection component (e.g. ozone, UV radiation), particularly if the water is to be used for laundry. Typically, treated grey water is used for toilet flushing and for watering the garden.  

At Archetype House A, a BracTM greywater system collects and treats water from shower drains, which is then used for toilet flushing.  At the Earth Rangers Centre, grey water and black water (sewage) is processed at an onsite treatment plant to make it suitable for reuse where possible.  

This technology is highly beneficial as a water conservation measure as it not only reduces loads to costly sewage treatment plants, but also reduces the amount of treated municipal water a household requires.  

For more information on this technology, visit Health Canada’s Canadian Guidelines for Domestic Reclaimed Water for Use in Toilet and Urinal Flushing page.