Re-using greywater in your household can be more complex than simply harvesting rainwater. There are plenty of products on the market, and they vary in technological complexity.
To help sort through the complexity, it is important to bear in mind that while there are many variations on each theme, there are essentially just three types of greywater systems:
(i) Simple diversion systems which can include mere bucketing of water from the shower or bath, but are more often a diversion valve fitted to an external pipe with connection to irrigation piping/hoses/drippers. Under EPA requirements these are intended for temporary use in dry weather
(ii) Permanent, pump assisted diversion systems with sub-surface irrigation to various parts of the garden
(iii) Treatment systems that provide advanced filtration and disinfection enabling storage for potential re-use both inside and outside the house.
Not surprisingly, costs are also variable with a wide spread of initial capital costs. In addition, some greywater systems have ongoing costs and issues associated with their maintenance and operation.
Greywater - Definition
Greywater can make up an important component of attempts to reduce mains or potable water use, as has been demonstrated most graphically through the work done at the home of Stuart McQuire in Brunswick, the author of Water: Not Down the Drain (CSIRO Publishing, 2008).
Greywater is generally considered to be the water that is discharged from:
- Showers and baths (can also contain soaps, shampoos, hair, skin, oils, faecal matter and urine)
- Washing machines (can also contain soaps, detergents, water softeners, bleaches, lint, dirt and small amounts of skin and faecal matter from clothes or nappies and is also the source of most of the phosphorus and sodium salts in household water)
- Bathroom hand basins (can also contain soap, toothpastes, mouthwash, shaving cream and hair).
By contrast, blackwater is considered to be waste water that must be connected to sewer and derives from toilets.
In the case of kitchen sink and dishwasher waste water, the potential for it to contain oils and fats that may clog re-use irrigation systems and effect soils means that, even in the absence of any health concerns, its incorporation into a greywater system is not recommended. Kitchen water only makes up around five percent of total water consumed in the average home, so its exclusion from greywater collection is a negligible loss.
It is also wise to exclude the washing machine waste water from greywater collection on the basis of excessive lint loads and their potential to clog sub-surface irrigation systems. Should that be the preference of the householder, then it also becomes questionable whether collection of water from the final washing machine rinse cycle is included in the greywater re-use system, as the amount of water collected could be comparatively small, although this may depend on the type of machine (top loaders use more water) and the number of washes per week. A simple diversion system from the washing machine discharge pipe on the outside wall to the garden – one that needs no permits – may be much more cost-effective providing there is gravity to assist with diversion to the garden.
Similarly, hand basin waste water may not be worth collecting compared to the extent to which it contains contaminants that could clog the re-use system. Click here for more information on this topic, and a link to the Master Plumbers Association Handbook and especially p. 46 - Best Practice Management Control Measures – Untreated Greywater.
Greywater – Potential for Replacement of Potable Water
As indicated in the introduction to the Water section of this website, based on the figures derived from the Central Region Sustainable Water Strategy (DSE, 2006), typical Melbourne households use 20% of water outdoors (mostly for garden irrigation), 14% for toilet flushing and 16% for clothes washing.
If a household was to choose a greywater treatment system (as opposed to a simpler, less expensive diversion system), then potentially all potable water across these three sectors – amounting to a substantial 50% of household use - could be replaced. Hence greywater can play an important role alongside rainwater harvesting in household water management.
Greywater – Regulation and Health Considerations
Greywater can be contaminated by pathogens which can cause illness to humans. Therefore care always needs to be taken if handling greywater or greywater plumbing (wear long rubber gloves), with washing of hands essential after coming into contact with either.
An increased extent of regulation applies to any in-house use of greywater, ie. for toilet flushing and cold water for washing machines. If greywater is to be used for these purposes, then according to EPA regulation, greywater needs to be treated to what is known as an advanced secondary treatment and disinfection stage and meet a 10/10/10 standard meaning a quality of <10 mg/L BOD5, <10 mg/L suspended solids and E.coli <10 cfu/100 mL. Greywater of this quality may also be used for surface and subsurface irrigation.
In order to guide greywater use, the Department of Human Services (Environmental Health Services) and EPA have both issued statements available at the following links:
EPA publication 884.1 Greywater use around the home – this is more of a summary document but includes the important do’s and don’ts information - and
EPA’s Code of practice:Onsite wastewater management - this is the more definitive document setting out specific requirements for various situations
The above should be referred to so that an appropriate understanding of greywater is established at the outset. See also:
Greywater – Weighing Up the Pros and Cons
While there are downsides to greywater use in terms of health and EPA requirements preventing storage for longer than 24 hours without treatment, the upside is that greywater is a much more reliable source of water than rainwater, especially in times of drought and climate change. Its reliability stems from the fact that its major source – shower and bath water (relatively clean sources of waste water) and washing machine waste, not only form a significant proportion (around 50%) of in-house use, but are also available every day a house is occupied. While the volume of water available for greywater re-use depends on the number of discharge pipes diverted to the greywater system it could be in the order of at least 120 litres per day based on a two person household using 45 litres (x2) for showers and an average of around 30 litres per day from clothes washing. This roughly compares to figures provided by the EPA on p. 24 of the Code of Practice document referred to above. The fact that greywater is also able to be directed to uses that comprise some of the higher uses of water around the home (ie. garden and toilet flushing) makes it doubly attractive.
However, in considering greywater systems (diversion and treatment), households need to carefully weigh up a number of factors including:
- long (if ever) pay back periods for expensive treatment systems. The expense is associated with the treatment technology in order to meet the EPA’s 10/10/10 standard (see above) where greywater is able to be re-introduced into the house for the washing machine and toilet flushing. Treatment systems also come with ongoing costs in the form of maintenance agreements with suppliers as is required by the EPA and ongoing maintenance
- the EPA notes potential discolouration of light-coloured clothes when greywater is used in washing machines (see footnote on p. 21 of the EPA publication Guidelines for Environmental Management: Code of Practice On-Site Wastewater Management). This may depend to some extent on the discolouration of the greywater when it exits the house – again perhaps avoid use of washing machine waste which could be the likely source of discolouration. This issue could also be addressed by installation of a cartridge filter prior to the treated greywater re-entering the house. See for example: http://rainharvesting.com.au/products/tank-accessories/rain-filter-systems
- there is some suggestion that odours from greywater used for toilet flushing may be an issue at times, although various products are available to combat this (see for example: http://www.enviropro.com.au/septic-system-revitaliser-ssr )
- although expected to rise at least 40% over the next four years, at $1.71 per 1,000 litres for Stage 1 users currently, potable water is still cheap. Assuming that it was available and not subject to restrictions, $15,000 (the rough cost of a treatment system) could currently purchase at today’s prices 8 million litres of potable water (an entire 2 person households’ lifetime of water - in excess of 70 years) and still be slightly more financially attractive than a greywater treatment system. For cost verification, see a positive case study cited by Choice
- especially where surface soils have high sand content, greywater that contains some oils (less likely in treatment systems or with buried drip irrigation) may exacerbate development of hydrophobia or water repellence. This has particularly been noted to happen where mulches discharge oils that coat soils, making water run off without being absorbed. This can be overcome by the working of compost into the soil thereby replacing and incorporating the sandy, water repellent layer. See: http://www.burkesbackyard.com.au/factsheets/Gardening-Tips-Books-Techniques-and-Tools/Adding-Organic-Matter-to-Soil/2923
- apart from a reduction in water bills, there are potential benefits for households around a sense of personal altruism and social responsibility to be derived from re-use of greywater
- having a thriving garden may add considerable value to a property thereby justifying investment in an expensive greywater system, especially if Stage 3 and above water restrictions were to become semi-permanent features of water supply in Melbourne over coming years and decades
- under Stage 3 type restrictions – assuming they become more commonplace again - use of potable water for garden irrigation is highly constrained. It should be remembered that at its most stringent level when introduced in April 2007 and continuing thereafter for three years, Stage 3a water restrictions meant that garden irrigation via a trigger nozzle hose could only take place for a two hour period in the mornings (6am to 8am) on two days per week (one day falling on weekends), while automatic drip irrigation systems could be employed on the same days between midnight and 2am only. These types of restrictions are possibly at inconvenient times for many, yet will no doubt be re-introduced at some stage should Melbourne experience another lengthy El Nino drought event such as that which just ended in mid 2010 after 13 years
- greywater is often nutrient enriched, as well as being warm water (where pumps discharge it to garden almost as soon as it passes into the storage area) and warm water – as opposed to hot water – is generally beneficial to plant growth
- the comparatively inexpensive nature of simple diversion (around $150) and even pump-assisted diversion systems (around $3,000) – it may therefore be possible, depending on the circumstances of the property, to employ one or a number (one for washing machine, one for shower and bath) of diversion systems at comparatively low cost that still provide complete replacement of the 20% of potable water that is used on garden irrigation by many households
- greywater can be ideal for establishment of a bog garden if your preference, instead of irrigating the whole garden, is to set aside an area in your garden for growing indigenous aquatic and semi-aquatic plants as a garden feature. These plants are very effective at taking up the nutrients contained in greywater. See further: http://frogs.org.au/vfg/features/greywater.php and http://frogs.org.au/frogwatch/greywater.php and http://oasisdesign.net/greywater/brancheddrain/index.htm also has some related material that may be useful. It should be noted that the extent to which such bog gardens comply with EPA Guidelines may be tenuous, as the EPA state that: “untreated greywater from the bath, shower and clothes washing machine can be bucketed or diverted to water lawns and gardens, as a temporary supply of water during dry weather.” Establishment of a bog garden may therefore need to demonstrate that it only requires greywater during dry weather and on a temporary basis, which is possible within a broad interpretation of the wording.
Installation of a greywater system also needs to be examined alongside other initiatives a household may be contemplating in order to save water (and household running expenses and energy). Investing in a front loading washing machine, dual flush toilets, tap aerators, low flow showerheads and a shower timer, an indigenous garden and a couple of shower buckets may all be items that show a greater return over the long term than a greywater treatment system. Available government rebates might also help with these purchases to a far greater extent than the $500 made available to house owners who install a greywater treatment system that could cost in the region of $15,000 (including installation) and with additional ongoing costs. Certainly if a household had a fixed $15,000 budget for water saving initiatives, then such an amount could potentially cover both installation of a reasonably sized rainwater tank, plus a greywater diversion system. These two initiatives together would be very likely to show a greater return than exclusive investment in a greywater treatment system and would involve less problematic issues.
A further set of factors for consideration in weighing up the extent of investment in greywater is its effects on:
- plants and soils – depending on the type of soaps, shampoos and washing powders and liquids used, it is generally considered that most greywater has fairly high alkalinity which will effect soil pH, which in turn may discourage growth of some plants (eg. Rhododendrons). However, soils with a pH of between 5.5 and 8.5 pose limited constraints for application of greywater. It is generally recommended that greywater is not diverted to the garden over winter (or longer, eg. April to October) in order to allow soils (especially microorganisms) and plants a chance for recovery from any ill-effects. It is also advisable to avoid concentration of greywater dispersal to one or a number of particular parts of the garden to again avoid over-burdening areas with greywater (see: http://www.savewater.com.au/how-to-save-water/in-the-home/greysmart/gardening-with-greywater). This can be done by turning on or off parts of the drip irrigation system, or by moving soaker hoses regularly to distribute greywater to various parts of the garden. Further information will be provided below regarding assessment of washing powders and liquids as this is critical to the success of greywater re-use as such products need to have low salt and boron content to be compatible with garden use on many plants. The exact effects of greywater on native and indigenous plant species is a topic that appears to have not been researched to any extent, so impacts are unknown – see: http://www.sgaonline.org.au/?page_id=5492# ; and
- clogging of sub-surface irrigation systems that are required by law to be used in order to irrigate gardens from permanent greywater systems – whether treatment or fixed diversion systems. Both lint and other contaminants from greywater can, if not cleaned out regularly, clog drip irrigation lines and soaker hoses. Some commentators have particularly strong views about this, see for example: http://oasisdesign.net/greywater/misinfo/index.htm#drip . Where households may not be able to find the time to undertake such regular cleaning of lines, perhaps initial consideration should be given to less maintenance-intensive systems (eg. bucket in shower, or a limited number of drippers). It should be noted that there are a variety of sub-surface irrigation systems and some claim to address the possible clogging of drip lines through different types of hose and dripper fittings with large orifice holes allowing large particles to pass through the dripper without blocking (see further below). Some go so far as to suggest that greywater is unsuitable for distribution through conventional low flow drip emitters (see for example: http://www.h2gro.com.au/Default.aspx?tabid=175 )
While the above encourages very careful consideration prior to investment in a greywater treatment system, none of the above should be read as outright discouragement of greywater re-use at the household level, especially as cheaper options with less complex technology can be employed to deal with greywater. Instead, the above is intended to merely encourage careful consideration of what is right for each household in an area where complex multiple options and a variety of technologies exist.
Greywater – Assessing Demand
The first step in order to prepare for working through these multiple options is to be sure of what use greywater can be put to. Do you want to invest in treatment so that greywater can be re-used in toilet flushing and for garden irrigation with better quality water? If so, try to calculate that demand for greywater based on a modern dual flush toilet using three and six litres for half and full flush.
If on the other hand, you want a system that is less expensive and merely for garden use, calculate how many litres of water your garden needs over summer. While this could be a potentially complex task requiring investigation of individual plants, perhaps you could simply run a calculation based on a hose discharge rate of 15 litres per minute and how long it would take you to give the parts of your garden requiring irrigation a soak once a week? A 40 minute soak could therefore possibly use around 600 litres of water. Coincidentally, a two person household showering for 5 minutes each with a 9 litre per minute showerhead would also generate a comparable amount of greywater - around 630 litres. Potentially quite a neat fit between demand and supply, even if the soaking with greywater is not possible due to the need to discharge every 24 hours. If you wish to include greywater from a bath include an additional 120 litres which is an average sized bath.
Looking at other more simple technologies, an indigenous garden with virtually no need for irrigation, could survive perfectly adequately on one or two 5 litre buckets of shower water on a regular basis over summer to encourage plant establishment and growth merely in the drier and hotter patches of the garden, or where some plants have for various reasons been planted beyond their natural range (ie. plants preferring wetter circumstances have been planted in conditions that become dry).
It should also be noted that the planting of large trees in any garden will cause moisture loss from soils if supplementary water is not supplied. If medium to large trees (indigenous or otherwise) are to be planted for shade, then consideration needs to be given to the effects on soil moisture which can in turn impact on house foundations and lead to cracking of internal walls. With such considerations in mind, greywater could be ideal to top up soil moisture especially during hot summers and in drought conditions.
However, in doing your calculations, if you find that your garden irrigation needs are much less (say 10 minutes once per week, ie. 250 litres) than the amount of water generated from shower and bath (say 750 litres based on 14 (7x2) five minute showers and 1 bath), then consider sticking with a bucket, as your garden could become excessively wet with the discharge of that amount of greywater, unless perhaps you regularly divert greywater to sewer in which case investment in anything other than a simple diversion device would be inadvisable.
In the heavy clay soils that are found within most parts of the City of Yarra, water retention could be a serious problem if excessive amounts of greywater are applied, although many gardens may well have modified soils that drain much more readily.
Once you have an understanding of the extent to which greywater could be used, the question then is the extent of sophistication of the response.
Greywater – Overview of Product Types
The following are various government and commercial websites that provide overview information on greywater systems.
As indicated at the outset, essentially there are three greywater system types.
(i) Diversion-only systems – these are simple (the most simple being bucket collection of water in the shower), cheap and usually require limited maintenance, although lack of pump assistance will often mean slow water flow and increased possibility of clogging of irrigation lines. Diversion-only systems involve diverting water with the aid of gravity from a discharging external waste water pipe through a hose or pipe into the garden. No permits are needed in Victoria for these systems as they are considered temporary and for use only in dry weather. These are often referred to as GDD-T, greywater diversion devices - temporary.
(ii) Diversion and filtration systems – these will generally have a removable filter which stops lint, hair and other particles from entering and clogging the irrigation system. They usually incorporate a submersible pump that sits in the bottom of the surge tank. They also often have a more complex irrigation system with sub-surface drip lines feeding greywater to various parts of the garden. They are therefore more automated than a diversion-only system. These are often referred to as GDD-P, greywater diversion devices - permanent
(iii) Diversion and treatment systems – these are significantly more expensive and vary from highly mechanised systems, such as aerated wastewater treatment systems, to sand filters. Treated greywater can be used safely in more direct irrigation systems, such as dripper lines, and inside the house for toilet flushing and laundry washing. They will also require varying degrees of ongoing maintenance and have running costs associated with ongoing water quality monitoring by the supplier. These are often referred to as GTS - greywater treatment systems.
All systems above nearly always use some type of greywater irrigation system.
Greywater – Product Options
1. Greywater Treatment Systems
The advantage of installing a treatment system is that the water will have a far lower nutrient and solids content as well as having a reduced pathogen load. As previously indicated, these systems allow greywater to be both stored indefiniely and re-introduced into the house for use in toilet flushing and in washing machines.
Examples of these systems can be seen at:
2. Pump Assisted Permanent or Fixed Diversion Systems or Greywater Diversion Devices - Permanent (GDD-Ps)
The advantage of these systems is that they provide pumping of greywater so the vast majority of the garden can be irrigated (even upslope areas), at a relatively even rate thereby ensuring good distribution of greywater. Pressurised pumping can also drive potentially lint-contaminated greywater through irrigation dripper pipes, although these systems also offer filter mechanisms to ensure that lint, hair and other impurities are trapped allowing drip irrigation to operate more effectively. However, concern over the longevity of inadequately maintained drip irrigation using greywater remains, but can possibly be overcome by use of a larger drip orifice as mentioned previously. A further type of pipe that addresses the peculiarities of greywater irrigation can be seen at the following link: http://sunshoweronline.com.au/products-more.php?catid=61&id=75
Examples of GDD-Ps can be seen at:
There are also others listed amongst products eligible for the $500 Victorian Government rebate at the following link: http://www.water.vic.gov.au/saving/home/greywater/rebates. All of these systems either pump greywater to the drip irrigation system almost immediately upon entry of the greywater or others simply pump to drip irrigation once every 24 hours. Therefore the size of the surge tank varies but is often less than 80 litres. It should be noted that there is unlikely to be ill-effects on plants from receiving drip irrigation if relatively hot water is pumped to the garden virtually straight from the shower. The drip irrigation, being set about 10 cm below the surface or under the mulch layer, should be in a relatively cool state in most parts of the garden.
3. Manual/Simple Diversion Systems
Diversion systems can be as simple as simply placing a bucket in the shower to capture cold water prior to hot water coming through and then capturing water during lathering, especially if you don’t have a device that turns water off at that time (eg: http://www.enviroshop.com.au/Every_Drop_Shower_Saver.html ). The water captured in this manner can be almost entirely free of soap and contaminants if the bucket is kept out of water drop during wash-off. A five minute shower could generate around 7-10 litres of water. This could be enough to irrigate a garden of drought resistant plants, even during the summer. It would certainly be sufficient to keep an indigenous garden thriving, even if it contains a couple of large shading trees (eg. a Blackwood on the west-facing side). The total cost of this system is the price of the bucket and your labour to distribute the water to the garden after every shower.
A slightly more sophisticated but still very simple and inexpensive option is a greywater diverter (see for example: http://www.enviro-friendly.com/greywater-diverter-valve.shtml or http://www.enviroshop.com.au/Waste_Water_Diverter_Valve.html or http://www.greentopia.com.au/store/p/2866-Platypus-Rainwater-Grey-Water-Diverter-Silvan-H2O.html?feed=au.shopping.com&gdfdomain=www.greentopia.com.au&gdftrk=gdfV2426_a_7c983_a_7c3779_a_7cPPDIVERT ) which can, where gravity assists, direct shower, bath and washing machine waste water to the garden via a potential variety of soaker hoses, pipes and splitter systems which can sit below mulch.
Such a system, due to gravity dependence, cannot be certain of reaching every corner of a garden, or raised garden beds. The total cost of this system is around $70 (excluding soaker hose or drip irrigation which may add another $100 or more, depending on the area you can irrigate via gravity), plus your labour to connect to a suitable soaker hose or pipe and drippers and maintain the hose. Note that, in the absence of filters, the soaker hose may block over time – perhaps even relatively quickly if connected to washing machine discharge. Also try to capture as much hair as possible in the shower grate before it escapes down the pipe. However, as the water is not filtered, these systems can clog up. Monitoring to ensure ground surfaces where flows are directed do not become waterlogged is also required.
Greywater - Irrigation System Equipment
While sub-surface drip systems used for mains water irrigation are often cast as being capable of use for greywater irrigation, there are a few notes of caution that need to be observed.
Firstly, it should be noted that to comply with legal requirements for sub-surface irrigation, dripper systems only need to be installed on the soil surface with mulch placed on top – not necessarily buried in the soil. This will help prevent potential for blockage from soils. However, burying drippers will direct moisture to plant roots more effectively.
Secondly, the pressure from pumped systems can help maintain clear lines. Thirdly, products such as Sulldrain drip tubing and Netfim pods can also help ensure effective performance of drip irrigation systems and may be able to overcome problems of clogged dripper systems.
Bathroom and Laundry Greywater-Friendly Product Options
As mentioned above, it is critically important to the success of greywater irrigation of gardens that greywater/garden-friendly soaps, shampoos and laundry products are used. There are various websites that provide analysis or an indication of salt content or other harmful chemicals (eg. boron) contained in these products. See the following links:
The Federal Government rebate program (the National Rainwater and Greywater Initiative) to encourage water conservation finished in May 2011. A Victorian Government Living Victoria Water Rebate Program continues and is available up until June 30, 2013. The program is split into two categories – one for small business and the other for home and garden.
Under the program a $500 rebate applies to the installation of a permanent greywater system. This includes all treatment systems and also most fixed or permanent diversion systems that are pump assisted. A list is provided at the following link: http://www.water.vic.gov.au/saving/home/greywater/rebates
It should be noted that the list is a fairly comprehensive one of a wide range of systems some of which can only be purchased from international suppliers.
The following provides a link to frequently asked questions about rebates: http://www.water.vic.gov.au/saving/home/rebates/home-and-garden-rebates/rebatesfaq
Council & Installation Requirements
If you plan to install a greywater treatment unit to enable storage and re-use of greywater you need to contact:
- Council's Building Services on 9205 5095 to ensure that it complies with current Building Regulations
- Council's Urban Planning department on 9205 5373 to check if you need a planning permit
- Council's Public Health Unit on 9205 5166 to obtain approval.
Installation of a permanent/fixed greywater diversion system requires installation by a plumber.
Water Management Officer
Back to top