Garden Bores
Background
Garden bores draw water from shallow groundwater, generally to about 50 metres in depth, although some can be as deep as 100 metres. This source of water is fed by rainfall which percolates into the ground across most of the Swan Coastal Plain.
The rain falls between the grains of sand and eventually stops at an impermeable barrier (for example rock or clay), trapping the rainwater to form “shallow groundwater”. Garden bores can provide a fit for purpose water source and can take pressure off scheme drinking water supplies.
It is estimated that there are about 164,000 garden bores in Western Australia, with about 90% in the Perth Metropolitan Area across the Swan Coastal Plain. These bores supply over 25% of all household water and use about 117 gigalitres per year – freeing up drinking water supplies to over 250,000 homes.
Some areas in Perth are unsuitable for a garden bore. These areas are generally:
- close to wetlands;
- near the foothills and places with clay or alluvial soils;
- within about 200 metres of the Swan River estuary or the ocean, including the Cottesloe Peninsula where salt water can be drawn into the bore;
- near industrial and waste disposal sites where groundwater may be contaminated; and
- in locations prone to acid sulphate soils.
The quality of water in a garden bore is different to that coming out of a drinking water tap. Generally garden bores produce water that contains natural impurities including brown colouration from plant saps, iron which causes brown staining and sulphur which can cause some odour. These substances are not harmful for garden watering.
Present Situation
Since February 2003 the State Government has supported the installation of garden bores through a rebate to people in areas where bores are suitable according to the Perth Groundwater Atlas (available online at the Department of Water’s website).
Over 21,000 rebates have been granted since the program began (about 5,000 a year). The total cost to the Government of these rebates has been approximately $6.5 million and they are expected to save approximately 37 gigalitres of scheme water over the life of the bores.
It has been a concern that some people overuse their garden bore. Excessive use of garden bores can lead to several problems including adversely impacting the sustainability of this shared resource. Overuse can also result in water quality problems (acids, nutrients, saltwater intrusion) and unnecessary energy use.
Garden bores depend on rainfall to recharge groundwater. As rainfall in the South-West of WA has fallen over the past 30 years, we need to use this resource wisely.
In October 2007, the State Government implemented permanent Water Efficiency Measures (WEMs) that impact the use of garden bores. In the Perth region, garden bores are now subject to a three day a week sprinkler roster system. This is adequate to maintain a garden without wasting water and avoids the risks of overuse.
The Future
Garden bores
In 2005, CSIRO completed a study on the opportunity for further garden bores in the Perth Metropolitan Area. A declining trend in groundwater levels was found in the northern coastal suburbs, central part of Gnangara Mound and around the Gwelup and West Mirrabooka areas. This study concluded that the opportunity for additional garden bores is highly variable across Perth (Figure 1).
The study found that by looking at the availability of shallow groundwater and demand for water for external use in the Water Corporation’s billing suburbs:
- 8% have a high opportunity;
- 30% a moderate opportunity; and
- 51% a low opportunity for more garden bores.
In addition, the Department of Water is currently updating the Perth Groundwater Atlas. Rebates for garden bores will no longer be available for areas deemed unsuitable for additional bores.
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Figure 1 – Relative opportunity for further garden bores (Source CSIRO 2005 ‘Opportunity for Additional Self Supply of Groundwater from the Superficial Aquifer beneath Metropolitan Perth’)
Community bore schemes
The Water Corporation has been working with developers, government departments and local councils to assist the development of waterwise communities.
A demonstration project at The Green in Brighton uses groundwater for outside watering (gardens, verges and eleven parks). This water is sourced from five community bores located in the development. This is considered to be a more sustainable alternative to separate garden bores as the draw on groundwater is monitored. To ensure that the amount of water taken is only what is needed the system is climate controlled through a centrally located weather station.
All new residents receive a Waterwise front and rear landscaping package which uses non drinking water from these bores.
The Water Corporation is working with the development industry to further extend this concept to connect to internal non drinking water uses such as toilet flushing and clothes washing.
Sustainability Considerations
Economic | Social and Cultural | Environmental |
| Less expensive than most scheme water sources. | Assists the community to maintain gardens and green spaces. | Consumes some energy through pumping. |
| The rebate provides incentive for householders. | Supports horticultural and leisure business. | May negatively impact wetlands through groundwater drawdown. |
| Provides fit for purpose use. | Positively impacts on property prices through maintenance of gardens. | May contribute to water quality problems if not adequately monitored. |
The Water Corporation has sought, and will continue to seek, to address the major sustainability considerations by:
- working with developers, government departments and local councils to promote the development of community bore schemes in suitable areas;
- working with the Department of Water to communicate to the public the need to use garden bores wisely;
- maintaining registers of known garden bores to assist monitoring;
- promoting garden bores in areas where they are suitable and can take the pressure off drinking water supplies; and
- administering the Waterwise Rebate Program on behalf of government and monitoring its effectiveness.
Potential source yield
The potential for garden bores is decreasing due to a number of factors, including:
- introduction of the three day a week sprinkler rostering system for bores;
- loss of rebate in some areas;
- smaller lot sizes making them less economical; and
- waterwise gardens require less water to maintain.
It is therefore estimated that about 2000 to 3000 new garden bores will be added each year (down from previous levels of 5000 a year). The Department of Water advises that prior to the impact of the 3 day a week permanent water efficiency measures, garden bores were estimated to use about 800 kilolitres a year each.
It is therefore estimated that the potential source yield of garden bores in the Perth area will be about 2 gigalitres a year. The potential yield from this source has been limited to a further 10 years at this time (2 gigalitres a year), due to uncertainty regarding rainfall and available superficial groundwater resources.
Cost
The cost to a householder of installing and running a garden bore is less than $1 per kilolitre.
More Information
- The Department of Health has a fact sheet on using bore water safely (331k.pdf)
- CSIRO Technical report on opportunities for further self supply
- Perth Groundwater Atlas
- Permanent water efficiency measures: Waterwise Ways for WA, Department of Water website,
Water Corporation website
Further information on garden bore use is available at the Department of Water's website
Key
Potential source yield (in 50 year planning horizon)
Potential cost (2007 $)