What is greywater?
Why use greywater?
Types of greywater system available
Are there risks in using greywater?
Use of untreated greywater
Maintenance essentials for a greywater system
Is reusing greywater worthwhile?
Greywater is wastewater from the following sources inside the home.
|Source||% of usable greywater||Is the water reusable?|
|• Showers, baths & spas||50%||Yes|
|• Washing machines||40%||Yes|
|• Laundry tubs||Yes|
|• Wash basins||10%||Yes|
* Reuse of kitchen wastewater (including from the dishwasher) is not recommended due to the likely presence of food scraps and fats.
Greywater does not include wastewater from toilets, urinals and bidets. This is referred to as blackwater and has too great a hygiene risk for safe treatment
A drying climate in Perth plus continued population growth is putting increasing pressure on our supplies of drinking water. Nearly 20% of our drinking water is already produced by expensive and energy-hungry desalination, and this will rise to one third over the next decade. Replacing drinking-quality water with greywater, where possible, has a number of benefits both for you as a homeowner as well as for the environment:
• Reduces your water bills
• Helps reduce overall demand for drinking water
• Reduces the volume of ‘clean’ wastewater discharged into the ocean or rivers
Each person living in an average Perth home produces around 120litres of reusable greywater per day, of which half comes from the bathroom.
Most domestic systems at a reasonable price do not treat greywater – in other words, improve the quality of the water - but simply divert it out of the waste pipe onto your garden. As such, it replaces all or part of your current garden reticulation system. Most homes run their sprinklers from their main drinking water supply – in a typical Perth home that accounts for over 40% of total water usage. If you already use a garden bore for retic, the advantage of using greywater is reduced. Remember that restrictions on sprinkler use also apply to garden bores.
Greywater systems basically fall into 3 categories:
For most homes, a Greywater Diversion Device or GDD is most appropriate as an automatic system.
1. Using a Bucket
You can freely use a bucket or siphon to collect and distribute your greywater before it goes down the drainage pipe (for example, collecting water from the washing machine’s rinse cycle, or whilst the shower is warming up). There are no restrictions or approvals required on the use of bucketed greywater – it can be reused for irrigation of gardens, lawns and outdoor pot plants, toilet flushing and in the washing machine.
Manual bucketing is considered a low risk activity because it involves low volumes of greywater, and hence any soil contamination is likely to be minimal and there should be very limited runoff to neighbouring properties or waterways. However, lifting lots of buckets of water may be bad for your back!
2. Using a Greywater Diversion Device (GDD)
A GDD is connected into the waste pipe (for example, from a shower). There is no storage or treatment other than filtering out of larger particles that may clog the system. The device incorporates a switch or valve to divert the greywater to the garden when required, and has an automatic overflow back into the sewer if this is closed. Greywater from a GDD must only be reused in gardens via sub-surface (ie, drip) irrigation.
Within the category of Diversion Devices there are 2 types, that vary in complexity and hence in price.
|Gravity System||None||Typically has a manual switch or tap. Greywater is diverted directly to a sub-surface irrigation system in the garden (ie, a network of dripper line some 10-15cm underground distributing the water to plants |
A gravity system will only work where the inlet is at least a couple of metres above the outlet, and may still lack pressure to effectively push water through a long dripper line
|Pumped System||Settlement and/or filtration only. |
This is not primarily to improve the water quality but to stop the pump and dripper lines becoming clogged
|Typically combines 4 elements: |
• Some filtration to remove larger particles from the water
• A surge tank to cope with sudden influxes of greywater (eg, draining the washing machine)
• A pump for distribution of the greywater directly into a sub-surface irrigation system
• A sub-surface irrigation system in the garden
Note that the surge tank in a pumped system is not a storage tank – greywater cannot be stored for more than 24 hours. A greywater system therefore cannot be used to build up a volume of water - like a rainwater tank for example. Some Diversion Devices pump all the water out every time the surge tank is filled. Other physically larger systems will hold the water for up to 24 hours (or until the tank is full) and then pump it all out. There are advantages to this approach - many plants grow better from having a larger drink less often as it encourages root growth.
Devices are available to automatically distribute the grey water to different watering zones so that each in turn gets the output from the surge tank, rather than one zone constantly receiving all the water.
3. Using a Greywater Treatment System (GTS)
A GTS is another step up in complexity (and hence cost) from a Diversion System. It both collects and treats greywater that has run down the fixture’s waste outlet to improve the quality, rather than simply filter out the lumpy bits. A GTS also needs a permit to install.
A GTS can work at several different levels, each lifting the quality of the output water.
If greywater is diverted before it enters the sewer system, it doesn’t need a permit for use and is easier to install. For example, washing machine wastewater pumped directly from the washing machine (preferably during the rinse cycle), collection of shower water in a bucket whilst it’s warming up, and siphoning water from a bath or laundry trough.
Where wastewater goes down the fixture’s waste outlet and is taken from the sewer pipe, a system to reuse that water does need a permit, must be approved by the WA Health Department and must be installed by a licensed plumber. I will take care of all those requirements for you.
Within these 3 categories there are a lot of physical differences in the systems on offer and a very wide range of prices. The needs of most domestic users can be met most cost-effectively by a pumped diversion system. I'll explain the key differences between what's available and advise on the most appropriate to meet your needs, the amount of greywater you produce, and what you're prepared to pay.
It's not safe to assume that greywater is clean and safe for reuse for all applications so long as it doesn't contain “blackwater” or toilet water. Of course the government has a duty to point out the health risks in greywater reuse and you may think that these are over-emphasised in official documents. However, your greywater may contain high levels of the following:
Garden soil, microbes and plants can degrade and adsorb many of the contaminants found in greywater so long as they're not overloaded. Many nutrients can even be beneficial if they do not exceed plant requirements. However, inappropriate use of untreated greywater has the potential to harm your local environment by:
Some of the environmental risks associated with the use of greywater can be managed by careful selection and use of detergents and other household. Look for “eco” branded washing powders and cleaning products that say they’re good for the environment.
To reduce health and pollution risks it’s sensible to try and reduce the concentration of hazards in your greywater by:
A Greywater Diversion Device (GDD) does not treat the water in the sense of decreasing any health risk from exposure to it. Although you may believe that your shower water is perfectly good for use all over the garden, washing the car or even flushing the toilet, government regulations prohibit you from using it for anything else than subsurface irrigation.
How can I use this water?
The quality of untreated greywater is variable with time of day, time of year and where it comes from. Wastewater quality is highest from bath, shower and washing machine final rinse, and lowest from the kitchen. Somewhere in the middle is laundry wash water. Stored greywater will turn septic and start to smell.
If you install an automatic pumped system to save the effort of collecting your wastewater in buckets, then you can only use this water for the following:
|Can I use it?||What for?||How is it used?|
|Yes!||Sub-surface or drip irrigation installed 100-150mm below the surface||Letting the greywater flow through the soil adds an extra level of filtration and treatment|
You must use separate dripper line to any existing drip irrigation using scheme water for 2 reasons:
• To prevent cross contamination of drinking water
• Because the holes in standard dripper line will clog up from the solids in greywater
|Yes!||Covered surface irrigation||Using dripper line on the surface but covered by thick mulch, for example around fruit trees or vines|
|With care!||Watering of native plants||Our beautiful native plants are not only waterwise but rather fussy about what’s in their water. High levels of detergent (for example from ‘unfriendly’ washing powder) could kill them|
|No!||Sprinklers||Spraying water over lawn or garden is not permitted. In any case, this is a very wasteful method of watering due to high losses from evaporation and windage|
|No!||Surface watering of leafy vegetables or fruit trees||Contamination risk|
|Check!||Right across your property||Setback limits apply from property boundaries, buildings, pools, paving etc. and there are guidelines for the area of garden required to dispose of the greywater. These must be followed in order to get a permit granted|
Regulations say that your greywater should only be used in drier periods in order to stop the water table rising too far and greywater reaching the surface, resulting in saturated soil. Also that there must be an overflow mechanism to divert the greywater back into the sewer. But in Perth’s sandy soils there’s a good argument for using greywater in your garden all year so long as the detergent levels are low.
If you have bought a front-loading washer to save water, be aware that the detergent contains more concentrated chemicals than that used in a top loader. Check the "eco credentials" of the detergent you're using to ensure it won't affect your plants. Liquid detergents are generally better than powders
Once a Greywater system is installed, it must be maintained for the life of the installation.
Both the device itself and associated sub-surface dripperlines require regular maintenance, such as cleaning and replacing of filters, periodic removal of sludge from the surge tank, periodic inspection of the subsurface distribution system, and checking of the soil conditions. The filter screen on the inlet of the GDD is very important as it removes a variety of materials (lint, hair etc) that may clog the pump or pipes. If the screen becomes clogged, the reticulation system will not work effectively.
Creative Clearwater Solutions can help you by planning or carrying out this maintenance programme
1. How much greywater do you produce?
A Greywater Diversion Device (GDD) is licensed by your local Council for your specific property, with the number of bedrooms being the primary indicator of the volume of water likely to be produced - rather than the number of people currently living in the property. For example, if a couple live in a house with 4 bedrooms, the system will still have to be scaled to accommodate 5 people.
60% of the greywater available for re-use from the average 4 person Perth household comes from the bath and shower. Another 24% comes from the washing machine. That adds up to around 3000 litres of greywater per week. In sandy soils all that greywater can be safely absorbed by only 80 square metres of garden. Even with a large modern house on a small block this area should be available, and this area could include the verge after allowing for setbacks.
If insufficient area is available, then the amount of greywater diverted to the garden will have to be reduced – for example by not using water from the washing machine.
2. How much is it worth?
The average Perth household uses over 40% of their total water consumption on the garden, which currently costs around $200 per year in water charges. Of course every household is different in terms both of size and their water consumption, and exactly how much of this purchased water can be replaced by using greywater depends on several other factors including the size of your block and your garden area.
It would be reasonable to assume $150 of water savings at current prices for the average household. Taking into account rising water prices and the cost of purchasing and installing a mid-range greywater system, the break-even point could be reached in around 15 years. Let Creative Clearwater calculate savings for your household!