Rainwater tanks help Australians conserve water, but new research has found some contain potentially harmful bacteria and elevated metal levels.
Researchers from Adelaide University and Flinders University tested 100 household tanks across Adelaide and
the Adelaide Hills.
Campylobacter was detected in 13 per-cent of tanks, Pseudomonas aeruginosa in 12 per-cent, Salmonella in 10 per-cent and Shigella in three per-cent.
Bacteria were also found in tanks supplying drinking water.
Of the households surveyed, 67 per-cent used tank water for drinking and cooking.
Lead researcher Dr Mira Cooper said rainwater could collect contaminants as it travelled across roofs, through gutters and into tanks.
“Rainwater might look clean, but once it lands on a roof and flows through gutters and into a tank, it can pick up bacteria, metals and other contaminants,” she said.
Dr Cooper said the findings did not mean people drinking tank water would necessarily become ill, but they
revealed potential hazards requiring greater attention.
A small number of tanks also contained cadmium, lead, arsenic or manganese above Australian healthbased
drinking-water guidelines.
Metal tanks were more likely than plastic tanks to contain elevated metal levels.
Poorly maintained systems were also associated with higher concentrations.
Senior author Professor Craig Williams said water quality depended on the entire rainwater collection system, including roofs, gutters, tanks and plumbing.
Leaves, dirt, animal droppings and other material can accumulate and affect water quality, making regular
maintenance important—particularly for households relying on tank water for drinking.
Researchers also examined whether rooftop solar panels affected water quality.
An apparent association with elevated metal levels disappeared after tank type was considered.
No clear link was found between solar panels, bird activity and harmful bacteria.
Further research is needed because testing detected bacterial DNA but did not establish whether the bacteria were alive and capable of causing infection.
Published in the Journal of Environmental Management, the study is described as South Australia’s first comprehensive assessment of the microbiological and chemical quality of roof-harvested household rainwater.