Greywater Reuse
Wastewater that is generated from your bathroom sinks, washing machines, showers, and baths is called greywater. It is water that has been used and is therefore not clean but could be reused for some applications such as garden irrigation. Toilet water and untreated kitchen water is not greywater. This is called blackwater and must be disposed in your septic or sewer system! There are some health risks associated with greywater reuse, but careful design and consideration of these risks can avoid issues. Many local governments will not allow greywater reuse for this reason, and you should check the rules in your local area, however considerable opportunity exists with greywater reuse for those that are able and willing to do it.
How to Design a Greywater System
A common and generally safe way to use greywater is to divert it directly outside for irrigation of grass, ornamental plants or fruit trees. Greywater can also be used to irrigate your vegetable garden, provided it doesn’t touch edible parts of the plants. Subsurface irrigation is often the solution here.
However, careful design of your greywater system is essential. A good design will consider the following technical issues.
- How will the water be diverted from your point of use, into a greywater system (away from your septic system)?
- How will the greywater be stored for later use? Is this necessary for your use?
- If you put a greywater tank in, can it be located at a point below the house such that the greywater can flow via gravity to it?
- How will you clean the greywater tank? Greywater is not perfectly clean and if it is untreated, it cannot be stored for long periods of time without risking algae growth. This may be a consideration for you.
- Perhaps a small storage dam would be preferable to a tank?
- Do you need a pump system to pressurise the irrigation system?
- The amount and quality of the greywater available may dictate exactly how it is used. You will need to design the downstream also to understand the demand.
- If your greywater storage becomes full, how will it be delivered back into your normal septic wastewater system?
- If your greywater system is empty, when you need to irrigate, can you divert potable water to it?
- Depending on your greywater use and demand, you may need to consider treatment and disinfection. Various technologies exist to treat greywater so that it can be stored for much longer periods and used safely for surface watering and other applications.
Issues to Consider
As mentioned above, your local regulations may dictate specific requirements around greywater reuse. This may include specific technical requirements, or the need for a specialist designer and registered plumber to undertake the works. Unfortunately, some local governments will not allow greywater reuse at all. Check your local requirements.
If there is any interaction between your greywater and potable systems, you must avoid back siphoning. There cannot be any risk or greywater getting into the potable supply. For example, you cannot simply connect a potable and greywater supply to an irrigation pump in case the greywater siphons back into your potable supply. You may need to consider back flow prevention devices or avoid this kind of interaction all together.
Also, if you are designing a greywater system that will be used for irrigation, you must make sure you are only using plant-friendly products within the house (bathroom and laundry), for example, those without too much salt, boron, chlorine bleach, or other harsh chemicals. These chemicals can build-up in your soil overtime and can harm the plants.
A Final Thought...
Greywater reuse is an excellent way to conserve water and reduce your dependence on utility supplied water. Carefully planned irrigation with greywater is a common practice in many places and can be done safely. Most households waste a considerable amount or reusable water every day, and if it can be reused in accordance with local regulation and good design, this just makes good sense.
To learn more, check out our in-depth guide, Elevate Your Home’s Water Efficiency with a Greywater Treatment System.
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