Many areas throughout Australia are exploring the use of rainwater tanks to supplement potable water supply. Various Queensland councils and the State Government have provided subsidies for customers who install rainwater tanks and it is required that rainwater tanks (or equivalent water savings) are installed in new dwellings. To maximise water savings, a rainwater tank should be connected to as many household uses as possible.
There are three basic configurations for rainwater tank installation. The approach adopted for the tank configuration will dictate the size and cost effectiveness of the installation. For example for properties with high outdoor water use, a simple tank configuration can save a significant amount of water. In most applications however, the gravity flow from a tank will not provide sufficient pressure to deliver water to multiple end uses. The use of a trickle (or reduced flow) rate supply to top-up from the mains supply will improve the reliability of tank supply and achieve reductions to peak water demands but means that water in the tank is subject to water restrictions.
1. Simple tank installation with the tank having an outlet for garden use.
2. Rainwater tank connected to a range of non-potable uses via a small pressure pump to outside taps, the toilet and cold water outlet to the washing machine. A mains water connection is normally provided to supply the tank during dry periods and improve the reliability of the supply.
3. Rainwater tank installed for all uses, including drinking water. In areas where reticulated drinking water is available, Queensland Health Recommend that it is used for drinking water in preference to water from a rain tank.
Approximately 3 million Australians currently use rainwater for drinking with very few reported incidences of ill health. This is in spite of a number of reports that have shown that tank water often fails to meet microbiological guidelines for drinking water quality because of contamination by animal faeces, vegetation and air-borne pollution. The current view of many health authorities is that while rainwater from a well-maintained system is a useful source of water, additional treatment may be desirable, particularly in urban areas. If plumbed in to the potable system, back-flow prevention is an essential barrier to protect the potable system from possible contamination.
The risks to public health can be ameliorated with proper maintenance and the use of various types of treatment barriers. Proper maintenance involves the cleaning of gutters and downpipes and the checks of mosquito and vermin control. If water is only to be used for non-potable uses, then it is unlikely that any treatment will be required. If the end use of rainwater is extended to the hot water system, it may be useful to install additional barriers, however, the hot water system itself will provide a degree of protection. If water is to be provided for all household uses, additional treatment should be considered. This could include a “first flush” system to divert the initial scour of dirty rainwater and potentially ultra-violet disinfection.
Other maintenance issues that should be considered are:
Recent research by the Urban Water Security Research Alliance indicates that maintenance of tanks is often not sufficient to ensure their safety or even sustainability.
ARCHIVE UWSRA overview of raintank maintenance issues - Release Date 18-Nov-2011: - In 2011 the Urban Water Sercurity Research Alliance undertook research into issues about ongoing householder maintenance of rainwater tanks.