Greywater system buyers guide
Although many regions no longer have water restrictions, water is still a very precious resource in a country as dry as Australia. Greywater systems let you use water at least twice, which makes good environmental sense. Here, we look at what systems are available.
The Greywater Buyers Guide was first published in issue 130 (Jane-Mar 2015) of Renew magazine. Issue 130 is a sustainable cooling special.
The advantage of greywater is that we produce it on a daily basis. In many cases it can be diverted to the garden with minimal effort and cost in a number of different ways. You can opt for a low-cost DIY system using something as simple as a greywater diversion hose attached to your washing machine outlet. Or you might be considering installing a full commercial greywater system. Whichever way you go, there are a number of things you need to consider.
This guide highlights the main issues associated with greywater reuse. There are many choices available and there is no single solution for all circumstances. Therefore, the more research you do, the more suitable your system will be for your particular situation.
There can be many restrictions as to where systems can be installed. In some cases, especially for retrofits, installing a greywater system will require major works—this can make the system cost-prohibitive.
Greywater is any wastewater generated from your laundry (sinks and appliances), bathroom (baths, showers, basins) and kitchen (sinks and dishwashers), before it has come into contact with the sewer. It does not include toilet wastewater, which is classed as blackwater.
However, while kitchen and dishwasher water is technically greywater, unless you are treating it, it is recommended that you don’t use this water source. Kitchen water only makes up around five percent of total water consumed in the average home, yet it is considered the most contaminated. This is partly due to high sodium levels from some dishwashing detergents, particularly from dishwashers, solid matter such as food waste from rinsing dishes, as well as fats, grease and oils from cooking and cleaning, which can all damage soil structure if allowed to build up.
What’s in the greywater?
The chemical and physical quality of greywater varies enormously, as greywater is essentially made up of the elements that you put into it.
Generally speaking, 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 actually 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 your soil 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.
Salt build-up in soils, particularly sodium salts, poses perhaps the greatest risk associated with untreated greywater reuse. The accumulation of salts in the soil can damage soil structure and lead to a loss of permeability, causing problems for soil and plant health. The main source of sodium is powdered washing detergents and fabric softeners that use sodium salts as bulking agents.
Concentrated powders and liquid detergents generally have fewer salts than the average powdered detergent. There are many powdered detergents on the market that now have low or no sodium content.
For more information and a list of products that are greywater friendly, go to www.greysmart.com.au (see the resources section for information on this site).
Generally speaking, pH levels outside the optimum range of between six and seven affect the solubility of soils and hence plants’ ability to absorb essential nutrients. As most gardeners know, pH values range from one (acidic) to 14 (alkaline), with seven being neutral.
As untreated greywater is generally alkaline, if you have an acid-loving garden, you will need to consider the types of cleaning products you use—washing powders generally make greywater very alkaline, as do solid soaps, while liquid soaps tend to be more pH neutral. The pH of greywater can vary depending on the source—shower water is often fairly neutral compared to washing machine water, for instance.
Before you’ve even applied greywater, pH levels can vary from acidic to alkaline from one part of the garden to another. Given this variability and the likelihood of greywater raising the pH of your soil, it is advisable to regularly monitor the pH and condition of your soil. Acidic soils can be made more basic with calcium carbonate and basic soils can be made more acidic with sulphur. To monitor this, pH test kits and soil conditioners are available from most nurseries.
Although salt build-up and pH are of particular concern, there are other greywater components that can have an impact on your soil and plants. They include fats and oils from soaps and shampoos, disinfectants (including eucalyptus and tea tree oil), bleaches, toothpaste, hot water and sheer volume of water—leading to over watering.
For more detailed information on greywater composition, see section 2.4 Composition of Greywater in NSW Guidelines for Greywater Reuse in Sewered, Single Household Residential Premises (www.bit.ly/NSWGreywater) and Oasis Design’s Fecal Coliform Bacteria Counts: What They Really Mean About Water Quality (www.oasisdesign.net/water/quality/coliform.htm).
Greywater system types
There are three broad categories that describe greywater systems: diversion only, diversion and filtration, and diversion and treatment. Each system type has its advantages and disadvantages, and it will depend on your circumstances as to which system is best for you. For example, if you want to store greywater for later use or perhaps even use this water inside the house for either toilet flushing or laundry use, you’ll need a treatment system.
Alternatively, if you only intend to water your garden via subsurface irrigation, then a direct diversion or diversion and filter system may be adequate.
However, you must bear in mind that each system type has different regulations governing its use depending on which state or territory you live in.
Diversion only systems are the simplest and cheapest. They can be as simple as bucketing shower or laundry water onto the garden, adding a three-way valve to your shower or laundry wastepipe, or connecting a hose to the end of your washing machine’s wastewater hose.
However, be careful if using the hose-on-washing-machine method as you could potentially shorten the life of your washing machine pump, if you are pumping water long distances or uphill. Washing machine pumps are only designed to pump water short distances. For this application, larger diameter greywater hoses are a good idea; they are available in diameters up to 50 mm.
The other issue with pumping directly from the washing machine is that too much water can be delivered too quickly to one area. This can result in water pooling, which can be a health concern for children and pets who come into contact with the water. There is also the risk of greywater leaving your property, which can carry legal implications if it enters waterways or neighbouring properties. The preferred method is to send the laundry water to a ‘surge tank’ close to the laundry, which allows a large flow of water to accumulate which is then distributed slowly to the garden. This avoids the washing machine having to pump long distances and allows for slower distribution to your irrigation area. However, greywater must not be stored in the surge tank; instead, it must be allowed to run slowly onto the area to be watered. If not, it must be emptied every 24 hours.
The diversion-only method is generally adequate for limited, irregular use of greywater. However, if you want to use greywater on a more permanent basis, you would be wise to consider a system that delivers water at a more controlled rate via subsurface irrigation. This is normally done with a surge tank, which can be part of a diversion-only or a diversion-and-filtration system. Treatment systems will usually have a storage tank that performs the same task.
Perhaps the one adequate diversion-only system is the Mulch Basin system written about by the Californian greywater guru Art Ludwig (see Irrigation section).
Diversion and filtration
Diversion-and-filtration systems involve filtering particles such as hair and lint before the greywater is delivered to its end use. Filtering is generally only required to keep particles from entering and clogging up your irrigation system. Hair and lint and even food particles are essentially compost and will decompose effectively in your garden, particularly if delivered below the surface into the active topsoil. Commercial diversion systems usually have lint filters that can be removed and cleaned periodically.
Most of the commercial diversion-and-filter systems have a surge tank that collects the initial gush of water and then delivers it to the garden in a regulated manner by either pump or gravity. The advantage of this is that the water is delivered at a slower rate, allowing the soil to absorb the water and reducing the risk of pooling, runoff and over-watering.
Diversion and treatment systems
There are a variety of ways of treating greywater, including biological, chemical and a combination of both. Treated greywater can be used in a wide range of applications, including laundry washing (in some states), and can also be stored—something that should not be done with untreated greywater.
Most treatment systems are expensive, usually in excess of $5000, and often require ongoing energy, maintenance and periodic water quality testing costs. Treatment systems may be ideal for some applications, especially where large volumes of greywater are produced daily and the gardens are big enough to utilise the water. However, it may be simpler and cheaper to use a rainwater tank for laundry water supply, combined with a simple diversion-and-filter system for laundry and bathroom greywater reuse.
Irrigation: using the water
In many respects, capturing and diverting greywater is the easy part of greywater reuse; distributing it through your garden can be more complicated and requires careful planning in order to deliver the right amount of water to each area. There are many irrigation alternatives that all have their pros and cons. Some of the commercially available greywater systems offer the installation of the irrigation system as part of the package.
One of the simplest ways to deliver greywater below the surface is through perforated pipe (agi-pipe), laid in filled trenches, 100 to 200 mm below the surface. Agi-pipe is flexible polyethylene pipe that has holes in it to allow water to seep out. Common diameters range from 50 mm to 100 mm, so it can easily be laid beneath the surface, even in narrow garden beds. Its flexibility also means it can bend around fairly sharp corners.
Agi-pipe should be laid on a coarse medium, if possible, such as gravel or recycled mulch. The pipe should slope down at a gradient of 1% to 2% (a slope of 10 to 20 mm every metre) to allow even distribution of the greywater.
If small volumes of greywater are being produced then lengths should be between 5 and 10 metres to allow the water to reach the full length of the pipe. If you are producing large volumes of greywater and have an area that requires longer lengths, then one method is to punch large holes every 300 to 500 mm in a large diameter hose (19–25 mm), connect one end of the hose to your greywater source and insert the perforated section of your hose into the full length of the agi-pipe. Depending on the pressure pushing the water, this should allow a more even distribution over a longer length.
Agi-pipe can be permanently connected to your greywater source with fixed piping, or you can leave one end of an agi-pipe protruding out of the ground at various points in the garden to allow a hose to be placed inside. This method allows more flexibility as you can also use rainwater or other water sources to water your garden, when available.
Some systems use dripper lines to deliver greywater. The advantage of dripper lines is that they are extremely efficient as they deliver water where it’s needed, at the root zone, and at slow rates that minimise wastage. This means that larger areas can be irrigated with smaller volumes of water. They are equally suitable for lawns and large areas of individual plants.
However, dripper lines require well-filtered greywater as the perforations in the hoses are very small and can clog easily. The average off-the-shelf dripper system is generally not suitable for greywater as the perforations are too small. However, some companies are producing ‘greywater suitable’ dripper lines, such as the Netafim Bioline range, that have bigger holes and other features that deal with the problem of clogging. However, most dripper lines will still need to be flushed out with clean water periodically.
Mulch basins are perhaps the only system of greywater irrigation that can deal with no filtration, potentially even from kitchen water (assuming sodium levels are kept to a minimum). It uses large diameter piping that can handle large organic particles and delivers the water directly to the mulch basin.
A mulch basin is simply a scooped out donut-like hole around the trunk of a tree, generally lined at the sides with rocks to stabilise the soil and covered with mulch to avoid people coming into contact with the greywater. The greywater outlet pipe is situated below the mulch but above the soil. The mulch acts as a sponge that soaks up the greywater and then slowly releases it.
The mulch significantly reduces evaporation, which can also reduce the likelihood of salt build-up and raised pH. Mulch also provides a medium for beneficial organisms to grow. Mulch basins are suitable for large trees, fruit trees and medium-to-large shrubs, and should be sized to accommodate the water surge volume they will receive. For more information see Art Ludwig’s book Create an Oasis with Greywater or www.oasisdesign.net/greywater/createanoasis.
How much water is required?
There are a number of calculations that can help you deliver the right amount of water to a given area.
Given the number of variables, such as soil permeability rates, rainfall patterns, plant needs and topography, it’s hard to look past the simple ‘finger’ method. Stick your finger in the first 20 to 30 mm of the topsoil; if it’s dry you need to water, if it’s wet you don’t. As any gardener knows, the best way to know how much water your garden needs is to spend time in it.
However, it is worth attempting to match your greywater output with your garden’s particular water requirements. This can be done by calculating your soil irrigation rate, the size of the area to be irrigated and seasonal variations, and matching that to your greywater volume, which can be calculated in a number of ways.
A good soil can generally absorb around 20 litres (about two buckets) of water per square metre and, depending on your plants’ needs and climate conditions, should only need watering once a week in summer and once every 20 to 30 days in winter.
As an example, a garden area that is 18 m2 would need 18 (m2) x 20 (litres per square metre), which equals 360 litres. If watering once a week in summer then this area would require around 360 litres per week. A shower with an efficient showerhead uses nine litres per minute. If two people had a shower each day for three minutes that would equal 54 litres per day. Multiply that by seven days and you get 378 litres per week, a fairly close match.
Alternatively, an efficient front-loading washing machine uses around 50 litres per wash (top loaders use around 150 to 200 litres per wash). If you did seven washes per week that would equal around 350 litres, also an approximate match for an 18 m2 garden area.
A useful document that covers many aspects of greywater reuse, including water calculations, is NSW Guidelines for Greywater Reuse in Sewered, Single Household Residential Premises. Although it was written for NSW conditions, it can be adjusted to suit other areas in Australia.
Do’s and don’ts for using greywater
There are some basic commonsense rules that have been developed to minimise the risks associated with greywater reuse. They include:
- wash your hands after watering with greywater
- divert greywater to the sewer during wet periods
- use garden-friendly cleaning products that are biodegradable and low in sodium and phosphorus
- don’t use greywater that contains disinfectants and bleaches
- don’t store untreated greywater for more than 24 hours
- don’t use greywater on vegetables and herbs that are to be eaten raw
- don’t use greywater sourced from washing nappies or soiled clothes
- don’t use greywater from the kitchen, unless it has been treated
- don’t let greywater leave your property
- don’t use greywater that is still hot as it will kill beneficial organisms in the soil.
It is important to understand what is required to install a greywater system on your property. Greywater regulations and permit requirements vary across Australia and you will need to check what the regulations are for your particular area. Permit requirements can even vary from one local council to another within your state or territory, so it is important to contact your local council first. Table 1 in the print version of the Buyers Guide (available here) summarises state and territory regulations and highlights the main relevant documents, but you should also consult your council to check in case of specific regulations for your local council area, or regulation changes.
There is no doubt that greywater is a valuable resource that we should be using, especially with summers becoming hotter and drier across most of the country. It seems crazy to waste our precious drinking water on gardens and lawns when there is a simple alternative readily available. What system or method you decide to use depends on many variables; there is no one system suitable for all applications. Whatever system you choose, you need to ensure that you manage its use correctly so that the real benefits continue to outweigh the potential negative impacts.
Table of suppliers and systems
A table of suppliers and systems is published with the print version of the article, available here.