The South Australian Government has introduced a number of initiatives, especially in recent years, with the purpose of encouraging and ensuring more sustainable water use in the State. One of these initiatives is the requirement for mandatory water tanks, which requires a rainwater tank and rainfall harvesting system to be set in place.
However, the compliance with this regulation brings out three important issues you need to be aware of: planning, plumbing and health and environmental issues.
1. Planning: When must you plan for a water tank?
Mandatory water tanks have to be plumbed in any new Class 1 development and any new extensions or additions to Class 1 buildings, whereby:
- Class 1 buildings are any single dwelling (a detached house) or one or more attached dwellings separated with a fire-resisting wall, and boarding or guest house, hostel or similar with a total floor area not exceeding 300 m2 and where a maximum of 12 people reside.
- Extensions or additions to Class 1 buildings that have roof area larger than 50m2 and that incorporate a water heater, water closer or laundry cold outlet.
The requirement for a plumbed rainwater tank for Class 1 buildings and their extensions applies to all areas of South Australia with the exception of Out of Council Areas, the Municipal Council of Roxby Downs and the District Council of Coober Pedy.
You can find a complete set of the technical requirements regarding the plumbed water tanks in the Building Code of Australia (Volume 2) – Part SA 2, and The South Australian Housing Code – Amendment 13 (Clause D. 11).
For additional information on the planning and building requirements, visit Government of South Australia Department of Planning website and search for additional requirements your local council might have.
2. Plumbing: What are the plumbing requirements?
SA Water sets the requirements you have to meet in order to enable seamless transition between the water supplies. This means that a continuity between the reticulated supply of water and the rainwater is required. You can achieve this by using one of the following methods:
- Installing a specially designed ball float control valve that is connected to the SA Water supply for supplying the water tank. This valve enables only a small amount of water to be let in the tank when it is close to empty so that the water supply to the outlet is ensured.
- By using a certified “watermark” device or valve which switches between the SA Water supply and the rainwater automatically. In this way, continuity of water supply to the outlet or fixture connected is ensured even when the supply of rainwater is depleted.
All the installations must be compliant with the Australian and New Zealand Plumbing and Drainage Standard AS/NZS 3500 and the SA Variations. The minimum requirements regarding plumbing installations that are associated with water tanks are:
- All the piping that delivers the rainwater to the fixtures, taps or appliances in the building must be installed by a licensed plumber.
- All the plumbing associated with the water tank must be made of approved materials (must have WaterMark Certification).
- The supply system from the water tank must be marked with the word “RAINWATER” with contrasting colour and at intervals not bigger than 500mm. The outlets must be identified with a “RAINWATER” label or a tap with green coloured indicator marked with the letters “RW”.
- If an outlet is supplied with rainwater, but backed up with the mains water to ensure seamless supply, it must be identified with the word “RAINWATER”.
- If a hot water heater is supplied with rainwater, the cold water inlet to the heater must be identified with the word “RAINWATER”.
Backflow prevention requirements
If you need to interconnect the rainwater supply with the mains supply, you must take into account the following requirements which apply under the AS/NZS 3500 and SA Variations:
- A backflow prevention device needs to be installed as a minimum for protecting the mains supply from the rainwater supply. Such a device is, for example, a “dual check valve” placed on the boundary of the property.
- In addition to the backflow prevention device (1 above), in cases when the rainwater supplies a toilet cistern only, a dual check valve or an air gap inside the cistern is required.
- A device (e.g. single-check non-return valve) is required on the pipeline from the water tank to prevent against uncontrolled mains water flowing into the tank (this valve may be incorporated into the automatic switching device).
3. Protection: Keep in mind hazard assessment
To make sure that health and environmental protection are being considered, you must have in mind protection assessments and take actions for reducing the potential hazards. The risk assessment you apply on the installed system should include at least the following:
- Assess the risk to the quality of rainwater from air pollution. For example, for dwellings that are located in industrial areas where it is very likely that roof run-offs contain pollutants, the water tank should be plumbed to the WC or the laundry cold water outlets.
- Assess the risk to rainwater quality from surface and/or groundwater. This assessment should contain the permeability of the piping and the tank, as well as of the joints to groundwater contaminants.
- Take precautions in the designing and installation of the rainwater harvesting system. There are a number of measures you can take including using appropriate materials, filters, gutter guards, dry inlets, first flush devices, guards against mosquitoes and vermin, ensure a quality maintenance program for the tank and associated piping system, etc.
- Take precautions in the selection and installation of the water tank to reduce hazard of contamination from surface and groundwater. In this case, the measures can include: careful planning of the tank location, structural integrity of the tank along with installation factors such as embedment, bedding, compaction, ensure the water tightness of the tank and all connections, joints and access covers, prevention from vermin by using self sealing valve, a reflux valve, a trap check valve, etc.
4. Certificate of Compliance
Last of all, don’t forget that you must provide a Certificate of Compliance to SA Water and the home owner within 7 days of work completion. The Certificate of Compliance is a form that needs to be completed by a licensed plumber. It ensures that the installation of the water tank and adjoining system is completed in accordance with the AS/NZS 3500 and the SA Variations.