Aside from the obvious benefits of saving water (and money on your water bill), reusing your greywater keeps it out of the sewer or septic system, thereby reducing the chance that it will pollute local water bodies. Reusing greywater for irrigation reconnects urban residents and our backyard gardens to the natural water cycle.
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:
- 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
Greywater, by definition, does not include the discharge of toilets or fecal contaminated wastewater of any kind, which is designated sewage or blackwater to indicate it contains human waste. However, under certain conditions traces of feces, and therefore pathogens, might enter the greywater stream via effluent from the shower or washing machine.
Sources of greywater include sinks, showers, baths, clothes washing machines or dish washers. As greywater contains fewer pathogens, it is generally safer to handle and easier to treat and reuse onsite for toilet flushing, landscape or crop irrigation, and other non-potable uses. However, the use of non-toxic and low-sodium soap and personal care products is recommended to protect vegetation when reusing greywater for irrigation purposes. The application of greywater reuse in urban water systems provides substantial benefits for both the water supply subsystem by reducing the demand for fresh clean water as well as the wastewater subsystems by reducing the amount of wastewater required to be conveyed and treated.
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, school or commercial building 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 often at household or building level. Larger greywater systems can treat and reuse large volumes of water, and play a role in water conservation in dense urban housing developments, food processing and manufacturing facilities, schools, universities, and public buildings.
Greywater Action is a collaborative of educators who teach residents and tradespeople about affordable and simple household water systems that dramatically reduce water use and foster sustainable cultures of water. Through hands-on workshops and presentations, we’ve led thousands of people through greywater system design and construction and work with policy makers and water districts to develop codes and incentives for greywater, rainwater harvesting, and composting toilets. We believe that decentralized conservation measures can play a critical role in drought resilience, climate adaptation, and the return of healthy stream ecosystems.