Greywater Recycling

Greywater Recycling Basics

What Is Greywater?

Greywater is any household wastewater with the exception of wastewater from toilets, which is known as blackwater. Typically, 50-80% of household wastewater is greywater from kitchen sinks, dishwashers, bathroom sinks, tubs and showers. Of course, if you use a composting toilet, 100% of your household wastewater is greywater.

Freshly generated greywater is not as nasty as blackwater, but if it’s not handled properly it can soon become so. Greywater decomposes at a much faster rate than blackwater and if stored for as little as 24 hours, the bacteria in it use up all the oxygen and the greywater becomes anaerobic and turns septic. After this point it is more like blackwater – stinky and a health hazard. In fact, many jurisdictions have strict regulations about disposal of greywater, some even require it to be treated as blackwater.

Not all greywater is equally “grey”. Kitchen sink water laden with food solids and laundry water that has been used to wash diapers are more heavily contaminated than greywater from showers and bathroom sinks. Although greywater from these sources contains less pathogens than blackwater, many regulatory bodies consider it as blackwater.

The safest way to handle greywater is to introduce it directly to the biologically active topsoil layer, where soil bacteria can quickly break it down, rendering the nutrients available to plants. This biological water purification is much more effective than any engineered treatment, thus protecting the quality of groundwater and surface waters.

The information on this page is used with the kind permission of Art Ludwig. Art is an ecological systems designer who has done extensive work with greywater systems. For more information, please visit his where you’ll find more than 300 pages of information about greywater, including greywater mistakes and preferred practices as well as the leading books on greywater.

Source: Greywater Recycling