Rainwater tanks are a popular way for Australians to save water, but new research has found they can also harbour potentially harmful bacteria and metals that could pose health concerns.
Researchers from Adelaide University and Flinders University tested rainwater from 100 household tanks across Adelaide and the Adelaide Hills, finding bacteria linked to gastroenteritis and other infections in a number of tanks.
The study found Campylobacter bacteria in 13% of tanks, Salmonella in 10%, Shigella in 3% (all linked to gastroenteritis) and Pseudomonas aeruginosa (which causes other infections) in 12%. Bacteria were also detected in tanks used for drinking water.
Two-thirds of the households surveyed (67%) said they used their tank water for drinking and cooking, highlighting the importance of understanding what is in the water people are consuming.
"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 along the way," says Adelaide University lead researcher Dr Mira Cooper (Beknazarova), a Flinders University PhD in environmental health. "We found potentially harmful bacteria in a number of household tanks, including tanks supplying drinking water.
"That doesn't mean people drinking tank water will become sick, but it does show that there are potential hazards that deserve greater attention."
The researchers also found small numbers of tanks contained levels of metals including cadmium, lead, arsenic, and manganese above Australian health-based drinking water guidelines.
Metal tanks (as opposed to tanks made from plastic) were more likely to have elevated metal levels, while tanks that had not been maintained well were also associated with higher metal concentrations.
The study, published in the Journal of Environmental Management, is the first comprehensive assessment of the microbiological and chemical quality of roof-harvested domestic rainwater in South Australia.
The article, 'From Roof to Tap: Emerging Public Health Risks in Harvested Rainwater,' analyses samples collected from 100 household rainwater tanks across Adelaide and the Adelaide Hills between May 2024 and January 2026. Researchers assessed water quality through microbiological testing, metal analysis, nutrient analysis and household surveys examining rainwater use and system characteristics.
The collaborative project involved research expertise in environmental health, microbiology, engineering, water quality and public health from Adelaide University, Flinders University, CSIRO and UNSW. It was supported by the HEAL (Healthy Environments And Lives) National Research Network, Australia's national research network investigating the health impacts of
environmental change.
