Rainwater collected from roofs and stored in household storage tanks can contain bacteria and potentially harmful metals, according to a study conducted in Australia. The researchers analyzed water from 100 storage tanks in Adelaide and the Adelaide Hills and found DNA of various bacteria associated with infections, including in systems used for consumption.
The investigation, published in the Journal of Environmental Management, detected Campylobacter in 13% of the tanks, Salmonella in 10%, Shigella in 3% and Pseudomonas aeruginosa in 12%. The first three are associated with gastroenteritis, while Pseudomonas aeruginosa can cause other types of infection.
Two-thirds of the households included in the study, 67%, said they used the water from the tanks for drinking and cooking, prompting the researchers to draw attention to the need to assess water quality along the entire collection system.
“Rainwater may seem clean, but after it falls on a roof and travels through the gutters to reach a tank, it can pick up bacteria, metals and other contaminants,” explains Mira Cooper, a researcher at Adelaide University and the study’s first author.
The presence of these microorganisms, however, does not necessarily mean that those who drink the water will become ill. The researchers emphasize that the analyses detected bacterial DNA, but did not determine whether the bacteria were alive and able to cause infections.
Metals were also detected
In addition to the microorganisms, a small portion of the tanks analyzed showed concentrations of some metals above Australian guidelines for drinking water.
Cases with elevated levels of cadmium, lead, arsenic and manganese were identified. The metal tanks showed a higher likelihood of elevated concentrations of these elements than plastic tanks, while systems with poor maintenance were also associated with higher metal levels.
The quality of the water thus depends not only on the rain, but also on the journey it takes to reach the tap.
“It is not only about what falls from the sky, but also about what happens to the water after it reaches the roof, the gutters, the tank and the piping,” says Craig Williams, professor at Adelaide University and co-author of the study.
Leaves, dirt, animal feces and other materials can accumulate in the collection systems and affect water quality, so the researchers emphasize the importance of regular maintenance.
Solar panels do not seem to explain the contamination
The study also analyzed whether the growing installation of solar panels on roofs could be related to changes in water quality.
In a first analysis, an association between the presence of solar panels and elevated levels of some metals was identified. However, this relationship disappeared when the researchers accounted for the type of storage tank used.
Nor was a clear link found between the presence of solar panels, bird activity and the detection of the bacteria studied.
The authors say further investigation is needed to understand whether the detected microorganisms truly pose a health risk. The study, conducted by researchers from Adelaide University and Flinders University, is presented as the first comprehensive assessment of the microbiological and chemical quality of rainwater collected from roofs for domestic use in South Australia.
