- Home
- Site Analysis
- Site Use
- Passive Design
- Water
- Minimising water use
- Stormwater controls
- Rainwater Systems
- On-site Wastewater Treatment
- Septic Tanks: Overview
- Septic Tanks: Design Checklist
- Aerated Wastewater Treatment Systems
- Disposal Systems
- Care and Maintenance
- Greywater: Uses and Safety
- Greywater: System Design and Installation
- Greywater: Gravity and Pumped Systems
- Greywater: Filtering and Treatment
- Greywater: Irrigation Systems
- Composting Toilet Systems
- Material Use
- Energy
- Health and Safety
- Other Resources
Water
Designing homes to use water efficiently, reduce costs and cope with more frequent droughts or storms.
Greywater: Filtering and Treatment
Greywater used for irrigation should be filtered. Greywater used for flushing toilets, should be treated and disinfected to minimise growth of micro-organisms in the cistern.
Filtration
If the greywater is not filtered it will tend to clog the irrigation system because it still contains high levels of solids. The inlet to the surge tank must have a filter to catch the lint (this can be as simple as a muslin bag). An alternative is a system that allows solids to be conveyed without casing blockages – for example specifying larger diameter pipes and outfalls into mulch basins.
In a simple filtration device, such as the one illustrated, greywater is distributed by gravity flow into a tank containing the filter material. The filter consists of a top layer of pine bark, a separating filter-cloth and a sand layer. The water flows continuously through the filter and directly to the irrigation system. Owners must be advised to replace filter material every few months or when it shows signs of clogging. The used filter material may be composted. Manufactured units are available in Australia.
- Simple type of greywater filter
Unfiltered greywater will tend to clog an irrigation system. In a simple filtration device such as this, greywater is distributed by gravity flow into a tank containing the filter material. The filter consists of a top layer of pine bark, a separating filter-cloth and a sand layer. The water flows continuously through the filter and directly to the irrigation system.
Domestic greywater treatment systems
A domestic greywater treatment system reduces solids, bacterial numbers and chemical pollutants. Treatment processes can include filtering, settlement of solids, flotation and separation of lighter solids, anaerobic or aerobic digestion, and chemical or UV disinfection.
Any treatment device which stores greywater in a tank without further treatment is not recommended. The water will quickly become foul, the bacterial count may be very high and it will present a potential health hazard if used for irrigation.
Treating greywater for toilet flushing
Unless greywater is treated to reduce harmful bacteria to an acceptable level it should not be used for toilet flushing. Commercially manufactured systems that treat greywater to a standard for toilet flushing and/or irrigation are available in New Zealand. They consist of multi-chamber tanks which reduce solids by settlement, floating and filtering. The water is treated by chlorination or UV and is pumped to the toilet cisterns (check that the chlorination system is compatible with an on-site wastewater treatment if one is installed). The toilet cisterns should have an alternative potable water supply which can be turned on while maintenance is carried out on the greywater treatment system or when demand is higher than normal.
- Treatment of greywater in proprietary system for use in toilet cisterns and irrigation
Greywater used for toilet flushing should be treated to reduce harmful bacteria. Commercially manufactured systems which do this are available.
Safety
When treated greywater is piped within a house:
- specify that all pipework and outlets are identified with a ‘Non potable water’ sign in accordance with NZBC G12/AS1
- ensure cross connection with potable water supplies is prevented by means of a backflow prevention device in accordance with NZBC G12/AS1.
For your clients
To help your clients understand onsite wastewater treatment options, safety issues, and the importance of maintenance, refer them to www.smarterhomes.org.nz/water/on-site-sewage-systems and www.smarterhomes.org.nz/water/re-using-greywater.