Water re-use is the use of effluent water for beneficial purposes in landscaping, agriculture, industry and domestic systems. All waste water can be recycled via onsite or septic systems which treat waste water including ‘black’ or toilet water and disperse the water close to the source.
A greywater system can help you save drinking water by watering your garden with water from the bath, shower or washing machine. Greywater technology is progressing rapidly and will become more important as demands on our water supply increase.
Regulations
‘The Code of Practice for the Reuse of Greywater in Western Australia’ provides information on the requirements for the reuse of greywater in residential gardens. It provides guidelines for householders and persons wishing to design and market systems. For a copt of the guide visit the Department of Health website.
Developers interested in large wastewater reuse schemes for commercial or subdivision purposed are advised to refer to the ‘Australian Guidelines for Water Recycling: Managing Health and Environmental Risks.’ Visit http://www.ephc.gov.au/
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Types of greywater systems
The Department of Health provides a list and information on approved greywater systems. The conditions of approval may vary depending on the design, with some systems not being permitted in non-sewered areas, not accepting kitchen waste flows or being of a smaller scale.
There are two types of greywater systems for the domestic market that both require local government approval and state government guidelines for installation.
Note: As a landscaper you will be required to work with greywater applications and it is important to familiarise yourself with the systems available and suitable methods of dispersal.
1. Diversion systems
which are either gravity or pumped (laundry and bathroom only)
Gravity diversion device
A gravity diversion device incorporates a hand activated valve, switch or tap and is fitted to the outlet of the waste pipe of the plumbing fixture such as a laundry tub. Greywater is diverted directly to a sub-surface irrigation system in the garden.
Pump diversion device
A pump diversion device incorporates a surge tank to cope with sudden influxes of greywater for distribution of the greywater directly to a sub-surface irrigation system in the garden. The surge tank does not operate as a storage tank.
2. Treatment systems
which upgrade water quality and provide more flexibility in terms of re-use applications (can be used for kitchen water as well as laundry and bathroom).
3. Irrigating with greywater
- Drip dispersal systems are used for greywater, delivering a slow and precise application of water throughout the soil.
- Drip irrigation eliminates health risks associated with wastewater and reduces run off and ponding due to a slow application rate.
- Specially designed dripline is available for greywater irrigation. Pressure compensated dripline can be used for treated greywater and non-pressure compensated for greywater diversion systems.
- The principles for installing a drip irrigation system for greywater are the same as for general dripline apart from the specialised pipe which allows for larger particulate matter.
- It is essential that household laundry detergents etc. are compatible with greywater reuse.
Important considerations when using greywater
1. Good dispersal design is essential. Greywater volumes and averages should be matched to the area to be irrigated.
2. To ensure water balances are achieved in high and low evaporation periods of the year and with varying occupancy of the dwelling, supplementary water may be required to ensure security of supply.
3. When using greywater in heavier soils where saturation of garden soils of low permeability may occur during periods of heavy rainfall there should be a facility to divert the greywater to a sewer or alternative disposal method.
4. Regular maintenance of the drip system is essential – check the manufacturer’s recommendations
5. Treated rather than diverted greywater is recommended for turf. Some paspalum varieties such as ‘Velvetene’ are able to handle poor, low quality or recycled water. Treated water can be used with dripline with no problem as the individual emitters do not need to accommodate particulate matter.
6. Non-treated greywater on lawns using subsurface is problematic as the emitters
7. need to be larger and are therefore prone to root intrusion which the root inhibitor chemical is not able to deter.
8. Greywater is not for use on leafy edible crops – herbs, vegetables etc.
9. A licensed plumber is required to modify any plumbing work.
Rainwater harvesting
With dry summers in Perth, there is limited value in collecting rainwater for residential garden irrigation unless a large tank is installed. Standard domestic tanks (1,500L-3,000L) do not have the capacity to provide sufficient storage to last through the dry season.
The best way to utilise rainwater in our Mediterranean (dry summer/wet winter) climate is to connect a tank with automatic mains water backup to the toilet, basins and washing machine. This leads to significant water savings because rainwater is used through the wet months of the year when indoor use remains constant and regular rainfall refills the tank.
If space and budget permit large water storage systems can be installed for external use with a pump and drip system for garden irrigation.
