The Art of Greywater Recycling

Greywater is the name for 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.

Demand on conventional water supplies and pressure on sewage treatment systems is reduced by the use of greywater. Re-using greywater also reduces the volume of sewage effluent entering watercourses which can be ecologically beneficial. In times of drought, especially in urban areas, greywater use in gardens or toilet systems helps to achieve some of the goals of ecologically sustainable development.

The potential ecological benefits of greywater recycling include the following:

  • Reduced freshwater extraction from rivers and aquifers
  • Less impact from septic tank and treatment plant infrastructure
  • Reduced energy use and chemical pollution from treatment
  • Groundwater recharge
  • Reclamation of nutrients
  • Greater quality of surface and ground water when preserved by the natural purification in the top layers of soil than generated water treatment processes.

In the U.S. Southwest and the Middle East where available water supplies are limited, especially in view of a rapidly growing population, a strong imperative exists for adoption of alternative water technologies.

Most greywater is easier to treat and recycle than blackwater (sewage), because of lower levels of contaminants. If collected using a separate plumbing system from blackwater, domestic greywater can be recycled directly within the home, garden or company and used either immediately or processed and stored. If stored, it must be used within a very short time or it will begin to putrefy due to the organic solids in the water. Recycled greywater of this kind is never safe to drink, but a number of treatment steps can be used to provide water for washing or flushing toilets.

The treatment processes that can be used are in principle the same as those used for sewage treatment, except that they are usually installed on a smaller scale (decentralized level), often at household or building level:

  • Biological systems such as constructed wetlands or living walls and bioreactors or more compact systems such as membrane bioreactors which are a variation of the activated sludge process and is also used to treat sewage.
  • Mechanical systems (sand filtration, lava filter systems and systems based on UV radiation)
  • In constructed wetlands, the plants use contaminants of greywater, such as food particles, as nutrients in their growth. However, salt and soap residues can be toxic to microbial and plant life alike, but can be absorbed and degraded through constructed wetlands and aquatic plants such as sedges, rushes, and grasses.

Canadians are some of the highest per capita users of water in the world. According to Environment Canada’s “Freshwater Website” (, simple changes to water use habits and domestic equipment can reduce water consumption in the home by up to 40%. There are many measures and strategies that can make a significant contribution to reducing water use. Some are quite common, simple and inexpensive, whereas others are relatively new or ground-breaking. One that fits into this latter category is using greywater. There is a growing interest in using greywater within the context of sustainable water management. Other factors that contribute to the interest in greywater use include:

  • The opportunity to provide reliable water services in remote or environmentally sensitive locations;
  • Overburdened traditional water sources;
  • The rising costs of meeting drinking water treatment and wastewater discharge standards;
  • The potential to reduce domestic wastewater discharges to water bodies;
  • Seasonal water shortages and droughts (potentially exacerbated by climate change); and
  • Population movement to large centres, resulting in changes to the spatial patterns of water demand.

Despite the advantages of using greywater, it is normal that pathogens or chemicals in greywater may pose a risk to human health or the environment. Owing to these risks and the low cost of water in Canada, pursuit of water reclamation has been slow. At present, British Columbia is the only Canadian province to have enacted a greywater standard (Municipal Sewage Regulation) for a variety of applications, including for toilet flushing and irrigation (Government of British Columbia, 1999). Alberta legislation (Government of Alberta, 1993) allows the use of treated municipal wastewater for irrigation; in support of the legislation, Alberta Environment (2000) has produced guidelines to aid in evaluating projects. The Atlantic Canada Wastewater Guidelines Manual for Collection, Treatment, and Disposal includes a chapter on greywater use, with a focus on irrigation (Environment Canada, 2006). Other provinces use a case by- case approach to proposed greywater projects. In the absence of guidelines, some jurisdictions are using demonstration or test sites to explore water reclamation.

Several reports have concluded that guidance and leadership from senior government on greywater are needed to ensure that it is incorporated into future water management strategies. It has been noted that two major barriers to the adoption of water reclamation as a strategy are the lack of standards for plumbing requirements for non-potable water systems and the lack of national guidelines for greywater quality.

If you are considering installing a greywater system you need to have it professionally designed. Any greywater contains bacteria that needs to be used quickly and safely to make sure there is no hazard to the environment.

To know more about greywater and wants to watch this GREAT video of a designed greywater system that provides water for whole garden!

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