Gardening with greywater – water quality
Greywater is domestic wastewater from baths, showers, basins, laundries and kitchens. It does not include water from toilets.
It is important to be aware of the substances going into your greywater, as these may affect plants in your garden.
Note: Greywater generated from kitchens, swimming pools and spa pools should not be reused for irrigation.
On this page:
- Using greywater in the garden
- Storing and distributing greywater
- Detergents and other substances in greywater
- How greywater affects plants
- Greywater dos and don´ts
Using greywater in the garden
Greywater is an excellent additional water supply for your garden. For example, you can collect water from the shower in buckets and then use it to irrigate your lawn and plants.
A typical Australian house generates an average of 100 litres per person per day of greywater, which is enough to supply 1 mm of irrigation over 100 m2 of lawn.
Reusing greywater can reduce your household´s total water usage, which is particularly important in times of drought and water restrictions.
Storing and distributing greywater
You can control where your greywater comes from and where it goes. You also control what goes into it and how and when it is used for irrigation.
In Queensland, you may collect greywater and apply it to the garden using:
- a flexible hose connected to a washing machine outlet
- a council-approved greywater diversion device or treatment plant installed by a licensed plumber.
Greywater cannot be stored on-site for more than 24 hours unless it has undergone treatment in an approved system. Always check with your local council before purchasing and installing diversion devices or treatment plants to make sure that your area is zoned as suitable and that you have the correct permits in place.
Detergents and other substances in greywater
Greywater from laundries can contain very high levels of salts, particularly in the wash water as distinct from the rinse water. Applying greywater without dilution may cause damage to some plants and to the soil itself (particularly clay soil).
Not all detergents are suitable for greywater systems. You can obtain information about the chemical composition of a detergent from either the product label or the Lanfax Laboratories website (see ‘Further information’ below).
Substances to avoid
These substances should not be allowed to enter your greywater system:
- bleach and caustic cleaners
- detergents that advertise whitening, softening or enzymatic powers
- detergents that contain borax, chlorine, bleach or petroleum-based products
- garden chemicals such as herbicides and pesticides
- automotive products such as oils, greases and brake fluid
- paints and thinners
- kitchen products such as oils and food particles
- faecal matter, such as from nappies.
For health reasons, greywater is not recommended where there is a risk that its microbial components may be ingested. Do not allow greywater to contact the edible portion of plants (e.g. fruits and vegetables).
How greywater affects plants
Some of the components found in greywater (water, salts and nutrients) have no adverse effects on plants, and in many cases they can be beneficial to plant growth. Nitrogen is a key nutrient for plant growth that is commonly found in greywater.
In some cases, however, greywater contains chemicals in high enough concentrations to be damaging to plants. Certain plants, such as South African proteas and some Australian native species, are sensitive to even low levels of phosphorus. For these plants, choose detergents with either no or low levels of phosphorus.
Consult your local nursery to determine which plants may be damaged by nutrients and salts found in greywater.
Look out for signs of plant stress such as wilting, leaf rolling and leaf death. Plants under stress are susceptible to greater damage from other stresses such as high or low temperatures and wear. If you observe any of these stress symptoms, use only the highest quality greywater.
Note: Greywater may not always be the cause of plant stress. Sometimes the same symptoms are caused by other factors (e.g. root rot). Even the best quality greywater or rainwater will not stop the symptoms from progressing if this is the case.
Reducing the risk of damage
You can reduce the risk of salt damage to plants by:
- not applying greywater directly to the leaves
- choosing low-salt detergents
- using the correct amount of detergent for the task
- discarding greywater from the wash cycle of the washing machine and using only the rinse cycle water
- mixing laundry greywater with bathroom greywater, if possible
- regularly changing the location where the greywater is applied.
Excessive salts are difficult to remove from soils high in clay and can cause permanent damage to soil structure, causing water to pool on the soil surface. Do not apply greywater if this appears to be occurring. If salts accumulate they can sometimes be flushed from the soil with rainwater. Gypsum can help to remove sodium from soils that have had salty greywater applied.
Greywater do and don’ts
- check with your local council before purchasing and installing diversion devices or treatment systems to check zones and permits
- have a licensed plumber install your greywater diversion device or treatment system
- use laundry liquids rather than powders to reduce the salt content of laundry greywater
- use laundry detergents with little or no phosphorus or boron
- use only as much detergent or cleaner as is required for the task
- combine laundry and bathroom greywater
- use wastewater generated from the kitchen, swimming pool or spa pool for irrigation
- apply greywater to any food crops or edible portions of plants (e.g. fruits and vegetables)
- use greywater generated by the wash cycle of the washing machine, unless it is diluted with other greywater
- use detergents that advertise whitening, softening and enzymatic powers and those that contain borax, chlorine, bleach and petroleum-based products
- apply undiluted greywater to clay soils
- apply greywater to oversaturated soils