What you need to know about reusing greywater

/ Sustainability / By /

You’ve got a decent amount of green space in your front or back garden and the thought has probably crossed your mind to reuse water for your piece of green paradise. But storing used water in buckets and lugging them out into the garden everyday sounds like hard work, surely there’s got to be an easier way! I’m happy to say, yes there is! Keep reading below to find out more on how to reuse greywater. 

If you’re just starting out in learning how to save water, you might be thinking of how to reuse water after rinsing foods like fruit, vegetables, rice or water from steaming. This type of water is considered clean-ish as non-brackish water and relatively easy to store and reuse small areas like pot plants. Reusing greywater is a bit of a step up from that and involves a bit more on the technical side but once everything is set in place, you won’t have to think about anything more than turning on your tap. 

First of all, what is greywater and how is it different from the water that you rinse  vegetables with and the water that is used in the toilet? One of the main differences between the three when reusing greywater is what the water is being used for and therefore how it can be treated after it has been used. In a household, you can categorically divide wastewater into two terms: greywater and blackwater, based on where the wastewater was generated. Greywater is wastewater from:

  • Washing machines
  • Showers
  • Baths
  • Wash basin
  • Spa baths
  • Laundry
  • Tubs
  • Kitchens

Blackwater is wastewater from:

  • Toilets
  • Urinals
  • Bidets

Greywater is reusable wastewater and “sorting” through the wastewater is the premise for how greywater is reused. Read the top reasons on why to reuse greywater. 

So how might one go about “sorting” through wastewater? Well, it really isn’t as gross as it sounds. Due to modern day plumbing, all wastewater is plumbed directly into either a public sewer, a septic systemic wastewater treatment system. This means that greywater areas can be directed towards the garden whilst blackwater remains plumbed into the main sewer where it belongs. As the name suggests, a greywater diversion device (GDD) redirects the greywater in a household to be reused in the garden via a dripper system that feeds small amounts of water in a plant bed or the lawn. A small divertor tap is installed on the system to redivert greywater back to sewer when it is not in use.

Guide to reusing greywater

If your property is located in a sewered area there are three options for reusing greywater:

 

  1. Bucketing
  2. Installing a Greywater Diversion Device (GDD)
  3. Installing a Greywater Treatment System (GTS)

Each method of reusing greywater has its pros and cons, for example bucketing is suitable for transferring small amounts of greywater to lawns and gardens with minimal effort and cost however you should learn how to safely reuse laundry water to water your garden. On the other hand, installing a GDD or GTS is an investment with both being costly methods although continued use will reduce overall water usage costs for your garden. Choosing a GTS over a GDD however does require ongoing maintenance to ensure high water quality is achieved through disinfection treatments.

 

 

GDD

GTS

Sub-surface irrigation

ü

ü

Surface irrigation

û

ü

Toilet flushing

û

ü

Washing machine

û

ü

How does greywater water my garden?

Water flows through a greywater system and feeds through a drip line connection. The irrigation field is a dedicated area of connected drip lines to provide surface or subsurface irrigation. Surface irrigation is the application of water at ground level and includes the use of low-rise sprinklers, micro-sprayers and drip systems. Subsurface irrigation is the application of water where drip lines are located at a depth of between 100mm to 300mm below the surface of soil or mulch. Various systems are approved for different types of irrigation methods so it is best to look for a system that best suits how you plan to irrigate your garden and the size of the area. Just like a garden tap, it is important to ensure the divertor tap is turned off to avoid overwatering for sub-surface irrigation in the garden when not in use. 

Is there enough greywater to water my garden?

There are two main sources of greywater in a household, bathroom greywater and laundry greywater contribute about 51% and 42% respectively of total reuseable greywater volume. Greywater reuse systems can manage single households and commercial premises that produce up to 5000 litres of greywater per day. Greywater volume can also be calculated based on the usage of water per person in a household, the type of system (GDD or GTS) and the type of building.

Water usage and therefore greywater volumes can vary by individual households. On average, a household (consisting of three individuals) generates approximately 825 litres of water per day of which is roughly 120 litres of greywater per person. This consists of 40 litres that is produced in the laundry and 60 litres that is produced in the bathroom.

Can kitchen wastewater be reused in a greywater diversion device system?

Living an eco friendly lifestyle can be great for using biodegradable cleaning products in the kitchen however this does not exclude kitchen wastewater being contaminated by food particles, grease, detergents and pathogens. As such, no kitchen wastewater is permitted in a GDD. Instead, a greywater treatment system (GTS) is appropriate for kitchen wastewater reuse. Treatment improves the water quality which can then be safely used for irrigation. 

What products can I use in my greywater diversion device system?

As your household product waste is going straight into the environment (without treatment), it is important to avoid use of some conventional products containing ingredients that can affect soil structure and nutrient concentration. Follow these top tips to minimise the environmental impact when reusing greywater in your household:

  • Only use products with no or very low phosphorus content. Phosphorus is usually found as an active ingredient in washing detergents and is displayed as a percentage figure on the product label. Low content starts from 0.05% and can go up to 10% in some detergents. Less phosphorus in products means less chance of phosphorus reaching our natural water sources! Learn more about phosphate-free washing detergents.

Is my property suitable for greywater reuse?

A greywater system isn’t suitable for every property and a quick call to your local council or state government Water Department can provide further advice about reusing greywater being appropriate for your location. The following must be carefully considered to ensure the property has suitable site conditions and will be approved for use:

  • Using an approved system.
  • Sufficient land application area (area/s to be irrigated). The land application area required must be calculated to ensure there is enough land to distribute the generated greywater.
  • The number of persons living on the property including any ancillary accommodation (e.g. granny flat).
  • Any spa baths located on the premises.
  • It is possible for multiple dwellings to be connected to one common onsite greywater treatment system if they are located on the same property.
  • Systems are also available for commercial sites however the design for the irrigation fields must take into consideration the type of use for the area e.g. no irrigation is permitted in children’s play areas (lawns) and sites with vulnerable populations such as hospitals, aged care facilities, schools and retirement villages should only use sub-surface irrigation.
  • Household reuse of greywater from a GTS is not suitable for multiple dwellings on the same lot or commercial sites.
  • A GDD is not suitable for unsewered areas. One part of a greywater system is connected to sewer to divert excess when it is inundated with water.
  • The greywater system should be set back more than 100 metres away from any natural water sources including wetlands, streams, rivers, lakes, estuaries or other water sensitive ecosystems.
  • The system must also achieve the necessary setbacks and minimum area required for irrigation. This is to ensure that water is drained evenly efficiently around the irrigation area and to prevent compromising the foundation/footings of buildings or structures and to prevent greywater from flowing onto someone else’s property!
  • A greywater system cannot be installed within a proclaimed public drinking water source area (dedicated zoned areas) without prior approval from state government.
  • A greywater system is unsuitable if the proposed site for installation is in a known environmentally sensitive area.
  • It is important to determine soil type in the surrounding irrigation area and topography of the local area to determine the best absorption and avoid greywater directly entering groundwater. For this reason, a minimum clearance of 600mm vertical separation is required as a soil absorption zone surrounding the irrigation field.
  • Depth to bedrock or hardpan to indicate potential excessive runoff or water logging.
  • Slope inclination to indicate potential runoff and erosion.

How to calculate land application areas for a greywater system

Before an application can be submitted, the land application area for a greywater system must be calculated to ensure there is sufficient land available to cope with the volume of greywater that is likely to be generated by the household. The calculation can then be used to mark out the area on a scaled site plan with all setbacks in place:

Greywater volume per week (L/week) ÷ Design Irrigation Rate (mm/week) = Area required (sqm)

NB: The Design Irrigation Rate (DIR) measures the ability of soil to transmit water. In the above calculation, the DIR value has been taken from AS1547.

Soil category

Soil type

Indicative permeability

DIR

Indicative drainage class

(mm/day)

(mm/week)

1

Gravels & sands

>3.0

5

35

Rapidly drained

2

Sandy loams

1.4 – 3.0

5

35

Well drained

3

Loams

0.5 – 3.0

4

28

Moderately well drained

4

Clay loams

0.06 – 1.5

3.5

25

Imperfectly drained

5

Light clays

0.05 – 0.12

3

20

Poorly drained

6

Medium to heavy clays

<0.06 – 0.5

2

15

Very poorly drained

What are the minimum setback requirements?

The total land application area required must include and meet setback requirements. The setback requirements are measured as horizontal distances from the subsurface or surface irrigation area:

Setback area

Subsurface drip (metres)

Surface spray (metres)

Closed fence boundaries

0.3

0.5

Open boundaries (i.e. open fence or no fence)

0.5

1.2

Buildings

0.5

1.5

Retaining wall, embankments, escarpments

1

3m or 450 degree angle from toe of wall (whichever is greater)

Bores

30

30

Trafficable areas (e.g. paths, drives, carports etc.)

0.3

1.8

In ground potable water tanks

1

3

In ground swimming pools

1

3

What else do I need to know before applying for a greywater reuse system?

There are instances where the design of an approved system must be slightly altered to meet the criteria and conditions of a permit to use a greywater system. The most common unsuitable site conditions for a greywater system include:

  • Unsuitable soil type: Large particle soils like course sandy soil or gravel can cause rapid movement of water and directly enter surface water bodies. In this case, soils should be tested and a sandy soil mixture applied in the irrigation area. Harder or more dense soil types like clay and limestone can hinder water drainage causing the surrounding soil to be oversaturated. If the water movement through the soil is too slow, it may be necessary to replace the soil in the irrigation field with sand or combine the existing clay with sand to form a loam mixture. Where there is a large amount of limestone, the system may need to be relocated or the limestone completely removed and the soil replaced.
  • It is important to ensure there is a 600mm vertical separation between the soil absorption zone and water bodies (i.e. ground water source) to encourage sufficient capacity to filter nutrients and pathogens from greywater before reaching groundwater. Where this cannot be achieved, there are two common options: the design for the irrigation area is altered by adding soil to raise the irrigation field above ground level for the 600mm vertical separation; or a GTS is installed instead of a GDD to ensure water is treated to a better quality when it does enter groundwater.
  • Soils have a phosphorous retention index (PRI) to indicate the ability of soil to retain nutrients from water before reaching groundwater. The PRI can determine what type of system is suitable for your soil type if you live close to an environmentally sensitive area such as a lake, estuary or wetland. High nutrient content in greywater can be damaging to the plants and animals that thrive in this environment. Greywater systems must be installed 100m away from the water body or consider another treatment system that utilises specialised soil mixture to remove nutrients before water is drained.
  • Your property may be located in a high water table area (or seasonal water table) or it may be prone to flooding during certain times of the year (i.e. rainy/winter season). If this is the case, the irrigation field area can sometimes be oversaturated with water and the greywater is not able to be absorbed. This is where the connection to sewer comes in handy! A handle or tap is located in the weatherproof diverter box so at any time you need to redirect your greywater away from the irrigation field or vice versa, just flick the switch. Take note however, greywater systems should not be installed on damp sites.

How can I tell if I am in a high water table area?

The most accurate way to assess if your property or parts of your property is within a high water table area is to obtain an independent technical report including detailed information on soil profiles and structures. The following tips however can give you some idea of how close your property may be from the underground water table:

  • Contact your Council for more information on water table depth and topography in the local area. Typically, low lying areas are likely to be in a high water table area. Look out for your state department online resource with mapping tools to estimate depth to groundwater information. For example, check out the Perth Groundwater Map, sourced from the Department of Water and Environmental Regulation (DWER)/Government of Western Australia.
  • Note any ponding of water or areas prone to mild flooding after heavy rainfall/during the wet season.
  • Your property is located within a flood prone area.
  • Plant profiles such as Melaleuca species (paperbark trees) are present in the local area or on your land.
  • Your property is located nearby (e.g. within 100m radius) a natural water source (e.g. stream, river, lake, estuary, pond etc.)

What happens if my greywater system can only be located in an area uphill from my house?

Greywater travels from a household to the greywater system similar to the way wastewater travels to mains sewer. Gravity allows greywater to flow downwards away from the house to the irrigation area. A minimum gradient of 1:100 (for every one metre of irrigation line, there needs to be a gradual change in depth of 1cm) is required for gravity fed irrigation systems to allow for even distribution of greywater and prevent pooling in the surrounding area. When a garden or lawn area to be irrigated is located uphill from the house or the area is too flat to achieve sufficient fall, a pump device is installed with the GDD. The pump automatically works to pump greywater uphill from the diversion device to the irrigation area.

A pump device must be fitted with a backflow prevention device and alarm to prevent greywater flowing back to the house. The alarm is usually fitted inside the house (e.g. laundry) and sounds when a backflow incident is detected.

What maintenance is required for a greywater system?

Ongoing maintenance is required to ensure greywater systems are operating smoothly and prevent them from failing. Maintenance work for a GDD can be done without a plumber, just remember to wear rubber gloves and mask to protect yourself. Here are the most common maintenance requirements you can expect for a GDD:

System component

Maintenance

Frequency

Primary Filter (course particles)

Thoroughly clean filter to remove physical debris (e.g. sand, lint, hair etc.)

Weekly

Secondary filter (fine particles)

Replace filter

Approx. 6-12 months

Surge tank

Clear out sludge from the surge tank

6 months

Sub-surface irrigation system

Check water is evenly dispersed through the irrigation field (i.e. soil is wet after an irrigation period). Inspect for leaks and clogged drippers.

Weekly

Exposed dripline re-covered with mulch to a depth of 100mm

As required

Irrigation dripline

Check vacuum breakers and flush valves along driplines during operation. Remove parts and clean.

As required

Sensor probe (if applicable)

Clean probe for accurate readings and pump operation

Weekly

Pump (if applicable)

Inspection for blockages

Monthly

Full system

Apply a full system flush at the end of Winter, when water will be diverted away for the season. Open the manual flush valves and run high pressure scheme water through the irrigation system until the lines run clear.

Before Summer season

To check how your garden is responding to greywater irrigation, you should monitor the condition of soils and plants. An easy way to do this, is to get familiar with some common signs your garden isn’t thriving with greywater reuse. After purchasing your greywater system, be sure to take note of additional maintenance that that may be necessary in accordance with the manufacturer’s requirements. 

Gloves should be worn when carrying out maintenance work on a greywater reuse system. Wash hands with soap and warm water immediately afterwards.

Ok so if you’re ready to start saving water, where do you start?

  • Get an application to install a greywater system from your local Council
  • View a list of approved greywater systems for your State
  • Choose a manufacturer from the approved list and complete the application
  • Include a site layout plan as a supporting document for the application. The manufacturer, a plumber or a draftsman may assist you with a site plan at a cost (system technical specifications should be provided to the person drawing up the plans to be used as a guide). It is your responsibility to ensure all set back requirements are met prior to approval.
  • Submit the application to your local Council and wait to receive an approval/permit to install the system
  • Engage a licensed plumber to install the system (Note: connecting the sub-surface irrigation field to a GDD does not require a licensed plumber)
  • Book in a final inspection with the local Council to ensure the system has been installed as per the approved plans.
  • Once a Permit to Use has been issued by the local Council, the system is ready to be used!

Be sure to read our post to find out how much a greywater system might cost you.

The take home message: you can and should reuse greywater but do it right! To start small, here are a few Do’s and Don’ts when using a GDD:

Do

Don’t

Reuse greywater for sub-surface irrigation only (at least 100mm below the surface of soil or mulch)

Don’t reuse kitchen or toilet wastewater

Switch back the divertor tap to sewer after irrigation periods

Don’t store untreated greywater

Select environmentally friendly and biodegradable products low in salt, phosphorus, sodium, boron and chloride.

Don’t irrigate during rainfall periods or winter seasons

Think about plant types suitable for irrigation with greywater.

Don’t overwater

Monitor plant and soil response to greywater irrigation every month

Don’t irrigate on lawn areas that are readily accessible to children, people with low immune systems or pets

Consider applying a soil-rewetting agent every six months.

Don’t reuse greywater that may be contaminated with nappies or soiled clothing.

Ensure regular maintenance is undertaken, including cleaning the filter weekly and maintaining the soil or mulch of the irrigation area

Don’t reuse greywater after using products containing chemicals including cleaning products, hair dye, paint, machinery oil etc.

Don’t reuse greywater on plants with edible fruits or vegetables.

Don’t reuse greywater for washing.

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