At its simplest, a greywater system takes water that has been used in household cleaning tasks and diverts it for use on the permaculture garden. When the toilet is flushed, the bath emptied or the washing machine used, a greywater system prevents the wastewater from simply going down the drain and into the sewer system; instead pipes take it out to the garden where it is used for irrigation. Particularly if it is utilized in combination with a rainwater harvesting method, a greywater system could go a long way to providing all the irrigation needs a permaculture garden has. It has the additional benefits of limiting wastewater (and so lightening the load on the municipal system of pipes and treatment plants) and of reducing your water bills.
However, harvesting and using greywater is not quite as simple as just piping the water from the bathroom and laundry out onto the garden; there are several variables to consider before installing a greywater system.
Different states in countries like the U.S. and Australia may have different zoning laws and regulations related to greywater systems, as may local authorities These could be related to the relative proximity of public bodies of water, the degree to which locations are prone to flooding, areas of environmental protection, and other local considerations. In reality, instituting a greywater system on your property is unlikely to cause the authorities to investigate you. If you ensure that your greywater is adequately stored and judiciously used, you should be fine to make use of it, but it is certainly worth checking local regulation. Even if you are prohibited from diverting bathroom and laundry water onto your plot, you can still use other forms of greywater, such as utilizing bath water and water used in the sink to clean vegetables to irrigate your garden, as opposed to letting the liquid drain away. Indeed, as long as precautions are taken about the chemical load in products used in such water, these methods of saving water should be a regular part of your permaculture practice.
It is not advisable to apply greywater to edible plants if the liquid has not been filtered. The potential for human waste, such as fecal matter and skin particles, to contaminate the food should not be risked. If you want to use the greywater on edible plants, you need to divert it through a natural filter, such as a wetland. This will take out all the waste matter, and it can safely be used on all types of plant, including those producing food crops.
What you put in to a greywater system will invariably, to some extent, come out. So you need to be aware of what is in the products that go into the washing machine, toilet and shower. Some chemicals that are commonly found in detergents can damage your plants. Boron, for instance, may be an essential element for plants, but on in very small amounts. An excess of the chemical (more that that which is naturally provided in a well-composted soil) can damage plants. Chlorine is another chemical often used in household cleaning products. If it gets into the soil in large concentrations, chlorine can inhibit plants’ ability to take up nutrients, and limit the activity of microorganisms in the soil.
Even detergents that do not contain these harmful chemicals can still be detrimental to plants, because they tend to make the water more alkaline. Most plants prefer a soil that is slightly acidic, so may not thrive if the greywater cause the pH level of the soil to increase. You could divert the greywater to an area planted with some of the species that are tolerant of alkaline conditions – such as chickweed, goosefoot and chicory – or you could combat the alkalinity of the greywater by adding material that ups the acidity; animal manure and compost that includes coffee grounds are good options.
Greywater should be used on the garden within two days of leaving the house, and ideally within 24 hours. This is to prevent potentially harmful bacteria (pathogens), such as those found in fecal matter, from multiplying, which is more likely to occur if the water is left to sit. These bacteria are the same reason why permaculturists do not use human waste as compost on edible crops. If you are routing your greywater through a wetland for filtration purposes, this will help eliminate any bacteria that may be present.
If you are in a location that experiences cold winters, with the ground frozen to a depth of several inches, it can be impractical to use a greywater system. The frozen ground would mean that the water is not able to percolate into the soil, and if applied to the garden could runoff and pollute local water bodies. And as noted above, you should not collect the greywater over the winter for use in the spring, as this can lead to high levels of harmful bacteria. For permaculture gardeners using greywater systems in areas with such climatic conditions, it may be best to divert the greywater into the municipal drainage system or a septic tank during the winter.
If you want to use greywater in a drip irrigation system, you will need to ensure that it is filtered well before entering the pipes. You will need to install a very fine mesh filter on the pipe connecting your greywater system to the drip irrigation mechanism. This filtration is necessary to prevent material that could clog up the tiny holes in the drip system from getting in. Lint from clothes, hair from the shower or from the laundry, even things like paper that may have been inadvertently left in the pocket of clothes going through the machine can block up the irrigation system, preventing correct water flow and depriving plants of moisture. And given that many drip irrigation systems are installed below ground, it can be difficult to tell when or where a nozzle gets blocked until a plant begins to show signs of water deficiency.