Tank water is often so heavily contaminated with feces that it does not pass minimally acceptable standards for consumption, a new study has revealed.
Research presented in Queensland suggests about 40% of rainwater tanks contained "heavy amounts" of animal feces contamination that could lead to gastrointestinal disease. The findings come from a study of 560 homes tracked over five years.
It comes as authorities encourage more Australian households to take advantage of tank subsidies to cope with drought and be more environmentally sustainable.
Microbiologist Stan Abbott, director of the Roof Water Research Centre at Massey University in New Zealand, analyzed samples of roof-collected rainwater and found 41 per cent were heavily contaminated with feces.
"This contamination can lead to gastrointestinal diseases such as salmonella, campylobacter, giardia and cryptosporidium," Mr. Abbott said.
At least half the rainwater samples would not have passed the minimally acceptable standards for drinking water, he said.
"The likely sources of the fecal contamination were fecal material deposited by birds, rodents, possums and frogs either on the roof, in the gutters or in the water tank," Mr Abbott said.
Relatively few disease outbreaks linked to contaminated roof-collected rainwater have been reported, but specialists in the field believe there is massive under-reporting of such illnesses.
Professor Ted Gardner, an expert in water-wise strategies at Queensland Institute of Technology where the research was presented, said more than two million Australians depended on roof-collected rainwater for their drinking water.
Most lived rurally with the exception of Adelaide, where well over a third of residents had opted to use rainwater.
"People love rainwater because it's soft and apparently pure, but clearly it comes with more risks than many people realize," Prof Gardner said.
Experts recommended householders use downpipe debris screens, a first-flush diverter and regularly disinfect their tank to reduce the risk of contracting waterborne diseases.
"The risk of disease from roof-collected rainwater can be low if the water is visibly clear, has little taste or smell, and the collection of the rainwater is via a properly maintained tank and roof catchment system," Mr. Abbott said.