Pictured: Dr Mira Cooper
A new study of household rainwater tanks across Adelaide and the Adelaide Hills has found potentially harmful bacteria and elevated levels of some metals, including in tanks used for drinking water.
Rainwater tanks are a popular way for South Australian households to save water, but researchers say what happens after rain lands on a roof could be just as important as the water falling from the sky.
Researchers from Adelaide University and Flinders University tested 100 household rainwater tanks across Adelaide and the Adelaide Hills between May 2024 and January 2026 as part of a study examining the microbiological and chemical quality of roof-harvested rainwater.
The study found Campylobacter jejuni in 13 per cent of tanks, Pseudomonas aeruginosa in 12 per cent, Salmonella in 10 per cent and Shigella in three per cent.
Campylobacter, Salmonella and Shigella can be associated with gastrointestinal illness, while Pseudomonas aeruginosa can cause other types of infection.
Researchers also found that some of the tanks containing the bacteria were being used for drinking water.
Of the 97 households that completed the survey, 67 per cent said they used their rainwater for drinking, while 76 per cent used it for gardening.
However, the findings do not mean that people drinking rainwater from household tanks will become sick.
The researchers used quantitative PCR testing to detect bacterial DNA, meaning further research is needed to determine whether the bacteria detected were alive and capable of causing infection.
Lead researcher Dr Mira Cooper shared, “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.
“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 tested the water for metals and found that between one and four per cent of tanks exceeded Australian Drinking Water Guideline health values for metals including cadmium, iron, manganese, lead and arsenic.
Between one and 11 per cent also exceeded aesthetic guideline values for metals and other substances including zinc, manganese, aluminium and sodium.
Metal tanks were more likely to be associated with elevated metal concentrations, while the researchers also found that poorer maintenance was linked with higher metal concentrations.
The study also looked at whether rooftop solar panels could be contributing to contamination.
An initial analysis found an association between solar panels and elevated metal concentrations, but that relationship changed after researchers accounted for the type of tank.
After adjusting for tank material, households with solar panels actually had lower odds of elevated metal concentrations, while metal tank construction remained associated with higher concentrations.
The researchers found no clear link between solar panels, bird activity and the presence of potentially harmful bacteria.
Senior author Professor Craig Williams said, “Water quality isn’t just about what falls from the sky – it is also about what happens to that water once it reaches your roof, gutters, tank and plumbing.
“Regular maintenance of rainwater systems is important because leaves, dirt, animal droppings and other material can build up and affect water quality.”
Leaves, dirt, animal droppings and other material can accumulate around rainwater systems, potentially affecting the quality of the water collected.
The researchers say this will become increasingly important as Australian households continue to rely on alternative water sources amid climate change and pressure on urban water supplies.
Professor Williams added, “Rainwater systems are going to be really important for ensuring water supply for homes and gardens in Australia as our climate continues to change. So, for households that rely on rainwater for drinking, we need to make sure we understand any health risks and how best to manage them.”
The research, titled From Roof to Tap: Emerging Public Health Risks in Harvested Rainwater, was published in the Journal of Environmental Management in September 2026.
The study brought together researchers from Adelaide University, Flinders University, CSIRO and UNSW and was supported by the HEAL (Healthy Environments And Lives) National Research Network.
Rather than suggesting household rainwater is inherently unsafe, the researchers say the findings highlight the importance of understanding and managing what happens to water from the roof through to the tap.
For households relying on tank water, the study offers another reminder that keeping the whole system well maintained is an important part of protecting water quality.
For more information, click here.
Related
Previous articleCape Ballet brings its magnificent production of Swan Lake to Australia for the first timeNext articleMasterChef alum Sav Perera to join Lola’s Wine Bar chef David Vargas for a one-night-only feast
