Written by: Sara Dennis
In most of the United States all municipally supplied water (used in showers, sinks, toilets, factories, etc.) has been treated to meet federal drinking water standards, even though only some of this water is used for drinking. Then, if it goes down the drain (i.e. not used for drinking, irrigation or cleaning), it goes through the energy intensive process of wastewater treatment. This treatment is highly necessary and important for blackwater (used water from toilets, urinals, dishwashers and kitchen sinks), which has higher concentrations of bacteria that can be harmful. However, other wastewater, known as greywater (from showers, non-kitchen sinks, washing machines, etc.) can be easily used a second time, to water plants or flush toilets.
Approximately 50-80% of residential wastewater is greywater, finding ways to reuse portions of it can reduce stress on water and wastewater treatment plants. Reusing greywater can provide a 30% reduction in water use for the average household, and an even bigger reduction on a commercial scale.
Collection and Treatment
There are different methods of collecting and treating greywater onsite. Manual bucketing is the most simple and low-tech system for collecting greywater. This involves draining greywater into portable containers that you can use to irrigate your lawn, garden and/or potted plants. You could even just bring an empty bucket into the shower and using the leftover water to water plants. When using this method, you should ensure that the water does not form pools on the surface or run off the property.
Using plumbing to direct greywater is another easy, relatively low-tech and often cheap way to reuse greywater. Greywater is collected from washing machines, showers and sinks, then directed to an outdoor irrigation system. This can be easily installed with washing machines because they are not permanently connected to the home sewer system. The washing machine’s drain hose is attached to a diverter valve that can switch the flow of its greywater from the sewer/septic system to a greywater irrigation system (see image). Shower and sink systems can also be connected to outdoor irrigation systems through plumbing but may require a pump if a gravity-system does not work.
While it is much easier to use greywater outdoors, it is possible to treat greywater to be used indoors, for flushing toilets. This process routes the water through an onsite treatment system that removes suspended solids, and possibly uses a chemical treatment before the water is used to fill toilets. Additionally, there are some products and appliances that simplify the process of reusing water indoors. An example of this are toilet lids you can buy with a sink attached to them – the water you use to wash your hands is then reused for flush water in the toilet.
Things to Consider
Before making or installing a greywater system in your home, make sure to do some research. For instance, it’s recommended that greywater is used within 24 hours of collection or it should be emptied into the municipal sewer system. Additionally, if you use greywater for irrigation you should pay attention to the ingredients in your soap or detergent. Many soaps and detergents contain nitrogen, phosphorous and potassium, all of which are nutrients that plants can use. However, if a soap contains sodium, chlorine and/or boron, it can harm the soil and plants.
Using greywater is a great way to reduce your water consumption, however some local ordinances, statutes and plumbing codes prohibit the use of greywater. Make sure to check with your local authorities before installing a greywater system!
1. “Chapter 5 - Water Efficiency.” LEED Green Associate Study Guide, LEED v4 Edition, 3rd ed., Green Building Education Services, LLC, pp. 119–126.
2. “Greywater Reuse.” Greywater Action, greywateraction.org/greywater-reuse/.
3. Lamb, Robert. “How Gray Water Reclamation Works.” HowStuffWorks Science, HowStuffWorks, 4 Apr. 2008, science.howstuffworks.com/environmental/green-science/gray-water-reclamation.htm.
4. “Utilize Greywater.” Water Wise Supply, Water Wise Supply, 2019, www.waterwisesupply.com/education/greywater.