An ideal water supply?
Dr Peter Coombes of the University of Newcastle in Australia heads a research time in the area of rainwater quality. Following over a decade of research into the quality of rainwater collected from roofs, Dr Coombes has identify the potential for rainwater to be utilised far more extensively than many government regulators recommend. In fact, Dr Coombes’s research reinforces the view of many Australians that rainwater is an ideal supply for our water requirements.
Highlights from Dr Coombes’s research
- Unlike water catchment systems such as dams, which are subject to large losses of water, rainwater tanks harvest water efficiently during drought, thus reducing demand on water supply reservoirs
- There is more rainfall in urban areas and minimal water is lost form the roof to the tank
- Rainwater tanks complement mains water supply infrastructure. They’re underutilised if water is only used for irrigation. Maximum benefit occurs when rainwater is used indoors and outdoors
- Rainwater quality is ensured by a natural treatment chain in the tank that reduces the presence of bacterial and metal contaminants. Bacteria, organic compounds and chemicals form flocks that become biofilms on surfaces or settle to the bottom of the tank to the sludge. The processes of flocculation, settlement and biofilms in tanks act to improve the quality of rainwater. The majority of bacteria in rainwater tanks are harmless and from the environment
- Water quality monitoring has shown effective pasteurisation of rainwater to remove bacteria in hot water systems. Rainwater used in hot water systems set at >52 degrees Celsius was compliant with Australian drinking water standards
- Separation of the first “flush” of rainwater from the roof and gutters improves tank water quality
- Rainwater tanks reduce stormwater volumetric discharges by 39%
- Cost of rainwater varies from $0.30 kL to a benefit of 0.39 kL – considerably less than mains water
- Extensive analysis of literature and research has revealed that health concerns about rainwater tanks are significantly overstated. You are more likely to contract illness from drinking mains water compared to rainwater.
Important Rain Harvesting system design features
Stan Abbott is the Director of the Roof water Research Centre and a Senior Lecturer in Microbiology and Communicable Diseases at Massey University in Wellington, New Zealand. Stan’s research highlights the importance of incorporating good design features and regular maintenance for Rain Harvesting systems.
Highlights from Abbott’s research
- The risk of disease arising from roof-collected rainwater consumption can be low, providing that the water is visibly clear, has little taste or smell and, most importantly, the storage and collection of rainwater is via a properly maintained tank and roof catchment system.
- Deficiencies in the use of rainwater catchment systems and components include: lack of maintenance, inadequate disinfection of the water, poorly designed delivery systems and/or storage tanks and failure to adopt physical measures to safeguard water against microbiological contamination.
- A range of enteric pathogens has been found in roof-collected rainwater including Salmonella, Campylobacter, Giardia and Cryptosporidium. The likely sources of these pathogens are faecal material deposited by birds, frogs, rodents and possums, and dead animals and insects. These sources may be in the gutters of in the water tank itself.
- Rainwater users can reduce their risks of disease from contaminated rainwater consumption by adopting a regular maintenance routine and using a well-designed Rain Harvesting System.
- Keep roof catchments clean and clear of moss, lichen, debris and leaves.
- Cut back trees and branches that overhang roofs.
- Regularly inspect and clean gutters every 3-4 months.
- Clean rainwater tank inlet screens every 3-4 months.
- Inspect rainwater tanks annually and clean them out if necessary.
- Test water periodically.
Recommended design features
- Clean, impervious roof made from non-toxic material.
- No lead flashings or lead-based paints.
- Gutter guards/screens and first flush devices to intercept.
- Wire mesh (screens) to cover all tank inlets.
- A covered and light-proof tank.
- Tank taps or draw-off pipes that are at least 100mm above the tank floor or a floating arm draw-off valve.
- A tank floor which slopes towards the sump and washout pipe.
- A well-covered manhole for easy access and inspection.
Roof-collected rainwater can be made safe and potable so that it complies with strict international drinking water standards (Waller & Inman, 1982; Gould & McPherson, 1987). This is especially true when measures such as tank cleaning and the use of first flush diverters and coarse rainwater filters are undertaken.
In South Australia, 42% of residents mostly drink rainwater in preference to mains water without any apparent effect on the incidence of gastrointestinal illness (Heyworth et al. 1998).
To investigate the relationship between tank rainwater consumption and gastroenteritis in South Australia, a prevalence survey of 9,500 four year-old children was undertaken and this was followed up with a longitudinal cohort study of gastroenteritis among 1000 four to six-year-old children, selected on the basis of their tank rainwater consumption (Heyworth, 2001). This study found that in South Australia, children drinking tank rainwater were not at a greater risk of gastroenteritis than children drinking public mains water. In fact, the data suggest that those children drinking treated public mains water were at an increased risk of gastroenteritis.