Guidance on use of rainwater tanks
In a similar fashion to all drinking water supplies, rainwater systems need to be monitored. Monitoring of domestic rainwater tanks consists of a range of visual inspections rather than laboratory testing of rainwater quality.
The recommended regime of inspections and associated maintenance is not particularly onerous, but it is necessary for quality assurance. A proactive approach will prevent the development of problems that can lead to the deterioration of water quality. Tables 2 and 3 provide an overview of monitoring requirements and corrective actions.
Once a rainwater tank is installed, it is recommended that the following components of the roof catchment and tank be inspected at least every six months:
- Gutters – they generally will need cleaning as well as inspection. If inspection finds large amounts of leaf material or other debris, then the inspection and cleaning frequency may need to be increased.
- Roof – check for the presence of accumulated debris including leaf and other plant material. Accumulated material should be cleared. If tree growth has led to overhanging branches these should be pruned.
- Tank inlets, insect-proofing and leaf filters – if necessary these should be cleaned and repaired.
- Tank and tank roof – check structural integrity of the tank including the roof and access cover. Any holes or gaps should be repaired.
- Internal inspection – check for evidence of access by animals, birds or insects including the presence of mosquito larvae. If present, identify and close access points. If there is any evidence of algal growth (green growth or scum on or in the water), find and close points of light entry.
- Pipework – check for structural integrity. Sections of pipework that are not self-draining should be drained. Buried pipework, such as with ‘wet systems’, can be difficult to drain or flush. Where possible drainage points should be fitted.
- In addition to six-monthly inspections, tanks should be inspected every 2-3 years for the presence of accumulated sediments. If the bottom of the tank is covered with sediment the tank should be cleaned.
- Rainwater tanks can become a significant mosquito breeding site when they are no longer required or when they fall into disrepair. Tanks that are no longer required should be drained, cut up and removed to an appropriate waste disposal site.
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Initial inspection on moving into a house with a rainwater tankOn moving into a house with a rainwater tank all the above steps should be undertaken. In addition, a wider inspection should be conducted to gain an understanding of the physical characteristics of the roof catchment area, storage tank and any associated pipework including whether:
- the tank and tank roof are in reasonable condition with no obvious holes or gaps that would allow ingress of small animals, insects or light
- water in the tank is clear and has no obvious odours
- the tank inlet is protected by a leaf litter guard and that all permanent openings (inlet, overflows etc.) are covered by mosquito-proof screens
- pipework is either self-draining or has drainage points installed
- there are no cross connections with the public mains water. If there are, it should be confirmed that this has been done in accordance with local requirements (check with the water supply authority – see Section 7)
- there is no exposed preservative-treated timber, large amounts of uncoated lead flashing or lead washers used with roofing screws on the roof area supplying the tank
- there is a flue from a slow combustion heater and, if there is, that it is installed in accordance with Australian Standards.
Local, regional and state/territory health authorities can be a valuable source of advice and/or information on rainwater tanks including local and state/territory requirements.
Water quality testingRegular chemical or microbiological testing of domestic rainwater tanks is not needed, but rainwater used for any commercial purpose or for community-based supplies will require testing to verify suitability for drinking (see Section 11).
Microbial testing of rainwater from domestic tanks is rarely necessary and in most cases is not recommended. Water quality in rainwater tanks can change rapidly during wet weather and, during dry periods, the concentrations of indicator bacteria (E. coli) and faecal pathogen numbers decrease due to die-off (Edberg et al. 2000). Testing for specific pathogens is often expensive and is generally only warranted as part of an outbreak investigation. If there are strong concerns about water quality, chlorination of tank water is a suitable alternative to testing. If microbial testing is undertaken, the parameter of choice is E. coli as an indicator of faecal contamination. Tests for total coliforms or heterotrophic plate counts are of little value as indicators of the safety of rainwater for drinking.
Chemical testing should only be required in exceptional circumstances, such as in specific areas where there are concerns about impacts from major industrial or agricultural emissions. In these circumstances the chemicals of concern need to be identified before testing or large costs can be incurred with limited likelihood of successful detection.
Advice on the need for testing and analytical laboratories should be sought from local water or environmental health authorities; alternatively, information on testing and analytical laboratories in the local area can be found in the business telephone directory by looking under ‘analyst’. When testing is performed, results should be compared to the values contained in the ADWG.