Watering gardens with greywater – plants that like greywater

Why use Greywater?

Rainfall in WA has been declining since the 1970s and with the extended drought conditions in many parts of Western Australia, water issues are one of our most pressing challenges. Fresh water is a precious resource, and using and reusing it, wisely, is a key component of trying to live more sustainably.

One effective strategy lies in reducing the overall demand for fresh water, through water-wise landscaping, rainwater harvesting, water-efficient appliances and fixtures, and implementing manufacturing processes with lower water needs than conventional methods. But even after reducing water usage initially, a lot of the water that goes down the drain is essentially wasted and could be put to good use as grey water in the home and yard. It is estimated that just over half of household water used could be recycled as greywater, saving potentially hundreds of litres of water per day. We must, therefore, work together to reduce our water use and reuse water wherever possible and we need to be more aware of the benefits of greywater.

Greywater is the water that comes out of the drains of showers, baths, sinks, and washing machines and is distinctly different from black water, which is what gets flushed down the toilet. Greywater can be used for watering houseplants, landscaping, or even flushing the toilet, so it’s a resource we can use twice. The problem is that our modern plumbing doesn’t distinguish between the two, but instead combines them as sewage. So, unless we manually divert or capture it, greywater essentially becomes black water, rendering it useless until it goes through the municipal water treatment process.

Assuming we are not using harsh cleaning or laundry products, including chlorine and bleach in the laundry or bathroom, a greywater system can be an effective method of reusing this used water to water trees or other landscape plants. In so doing this helps to save our potable water supplies and reduces our home water usage and costs and supports a thriving landscape.

Greywater is generally good for plants

Greywater has a highly variable chemistry depending upon the activities of the residents and the volume of water and the products used for cleaning and washing. Research regarding the long-term impacts of greywater on plant and soil health is seriously lacking, so the effects of usage are, at this stage, are a bit of an unknown quantity. However, plants and soil work hard to break down greywater with the soil filtering out many contaminants through a basic process: As water passes through layers of sand or granulated rock, larger water contaminants are caught in the grit of the dirt’s solids. This process is like straining solids out of soup with a colander, on a smaller scale. (If this sounds farfetched, remember that one key component in commercial water filters is charcoal.) The dirt itself helps filter out nutrients and biodegradable materials, which can then be absorbed by plants and bacteria:

Microorganisms and bacteria in the ground feed off carbon and pathogens, leaving water, carbon dioxide and non-polluting insolubles.

The rest of the water, now purged of major pollutants, is absorbed by plants or seeps down to recharge the groundwater.

Greywater can:

Boost Plant Growth: Gardens can come alive with the sheer volume of greywater alone as it contains a wealth of micro-nutrients. One class of nutrients found in greywater is organic matter such as skin cells, phosphorous, found in most soaps and commonly used as a fertilizer.

Boosts Crop Yields: for the reasons listed above, greywater will make your crops bear fruit like never! And there is no need to worry about using “icky” greywater on food. Plants use certain elements found in greywater, such as phosphorous and nitrogen, after microbes in the soil have broken them down. Plants obtain these elements from manure in the same way. An apple tree fertilized by manure does not produce apples full of manure. By the same logic, crops grown on greywater do not contain “dirty” greywater. They contain components found in greywater that plants can absorb after microbes in the soil have broken them down.

Create A Cool Micro-Climate: abundant greywater will create a permanent oasis around your home. The daily flow of water will keep your landscaping from become arid. It will also promote the rapid growth of shade trees, which lower temperatures by providing shade and through evapotranspiration, and have been found to lower air-conditioning costs in detached houses by 20-30%. In addition, plant cover prevents the ground from absorbing too much heat. Many “sustainable” alternatives to lawns, such as gravel, pavement or turf, do exactly the opposite, absorbing the sun’s rays to create an oven effect.

Restriction-free water supply

In addition to saving water, greywater reuse ensures a regular supply of irrigation water that is typically consistent daily and not limited by water restrictions, resulting in greener gardens and landscapes.

How to reuse grey water

It’s important to remember that there are rules and regulations about grey water reuse and improper management of grey water can lead to odour, pest, or pathogen issues, so it’s important to use a greywater professional to install any sort of grey water system.

What’s in the greywater?

The chemical and physical quality of greywater varies enormously, as greywater is essentially made up of the elements that are put into it. Generally, pathogen and bacteria content is low in most greywater sources (unless you are washing contaminated items, such as nappies) and, provided you take steps to minimise potential contact, such as using subsurface delivery of the greywater, it is of minimal concern.Choosing the right cleaning products is perhaps one of the most important elements in reducing the risks associated with greywater reuse. The elements phosphorus and nitrogen are nutrients necessary for plant growth. If these elements are kept to a suitable level by choosing cleaning products with low phosphorus and nitrogen content, they can replace the need for fertilisers for gardens and lawns—the nutrients can be utilised by plants and soils.

The main concerns with greywater are salt build-up from cleaning products and increased pH levels in the soil. Both can have a detrimental effect on soils and plants. However, they can both be mitigated by monitoring, conditioning your soils for optimum health and taking care to choose cleaning products with little or no salt.

There are many plants and turf that like greywater
These include:

• bird of paradise
• melaleuca
• dietes
• gardenia
• callistemon
• confiers
• liriope
• yucca
• hibiscus
• manilla grass
• seashore paspalum
• saltwater couch grass
• st augustine turf*
• bermuda grass*
• buffalo grass*
• green couch*

Calculating how much greywater you can put on your garden

By far the easiest way to use greywater is on the garden. When you’re calculating how much greywater you can put on your garden, reckon on about 5 litres per square metre for sandy soils (20 sqm/person) and 3 litres per square metre for non-sandy soils (33 sqm/person).


• Keep an eye on the health of your plants. Greywater tends to be high in chemicals that alter the structure of the soil, and it also tends to be overused.
• Bear in mind: sick looking plants could be suffering from overwatering, rather than the chemicals in the greywater.
• Give your plants a break by using rainwater (if you have a rainwater tank) or tap water every six weeks.
• Use compost to increase the organic content of your soil, improve its structure

About The Author

Ken Higgins

Ken is a director of Complete Enviro Solutions (CES), a Western Australian owned family business founded in 2008 that provides a unique “one-stop shop” of consulting, sales and installation in the sectors of energy and water saving initiatives. We believe there needs to be a balance between these, which can be achieved through skilful and careful planning. Our mission is to provide sustainable products and services in an efficient and cost-effective manner to reduce the amount of energy and water consumed in residential homes and businesses. CES has supplied and installed all the rainwater systems in Landcorp’s White Gum Valley Project and consulted on the supply and installation of the greywater system installed at Bethanie’s Aged Care facility in Gwelup. CES has installed numerous other rainwater and greywater systems to individual homes as well as solar power systems including commercial applications. CES was responsible for the supply and installation of solar hot water systems to the City of Vincent.