Rural
6 October, 2026
Water testing can reveal hidden problems
New research on rainwater tanks found they can also harbour potentially harmful bacteria and metals that could pose health risks.
But a local scientist said some results needed qualification for long-standing rural situations.
Researchers from Adelaide University and Flinders University tested rainwater from 100 household tanks across Adelaide and the Adelaide Hills and found bacteria linked to gastroenteritis and other infections in several tanks.
The study found Campylobacter bacteria in 13 per cent of tanks, Salmonella in 10 per cent, Shigella in 3 per cent (all linked to gastroenteritis) and Pseudomonas aeruginosa (which causes other infections) in 12 per cent.
Bacteria were also detected in tanks used for drinking water.
Two-thirds of the households surveyed (67 per cent) said they used their tank water for drinking and cooking, highlighting the importance of understanding what people are consuming.
Lead researcher Dr Mira Cooper, from Adelaide University’s School of Physics, Chemistry and Earth Sciences, said the findings were a reminder that rainwater collected from a roof does not necessarily remain as clean as it appears.
“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,” she said.
“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 that a small number of tanks contained metal levels, 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.
Senior author Professor Craig Williams, from Adelaide University’s College of Health, said the research highlighted the importance of looking at the entire journey of rainwater – from the roof to the tap.
“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,” he said.
“Regular maintenance of rainwater systems is important because leaves, dirt, animal droppings and other material can build up and affect water quality.
“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 study also examined whether the growing use of rooftop solar panels could affect rainwater quality.
While an initial analysis found a link between solar panels and elevated metal levels, that relationship disappeared when the researchers accounted for the type of tank.
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.
Local opinion
Hamilton-based scientist Larry Walker has run a water testing lab for well over 20 years and agreed with the study in that it highlighted water quality often being an overlooked aspect of life on rural properties.
Still, his qualifications in analytical chemistry and real-world encounters with farmers and regional property owners had given him a somewhat different perspective.
He said the Adelaide study had merit but was, in most situations, likely “massive overkill” when simpler methods can usually reveal enough information to act on.
“My approach would be to actually just grow the bacteria and see how many physically stand up and wave at you, instead of converting it all into ... doing DNA extraction and quantitative PCR,” Mr Walker said.
He added using “a couple of hundred thousand dollars worth of gear to determine what the metal content is” was interesting, but there was more value in “looking for e. coli and coliforms as faecal contaminant bacteria”.
“The key drivers of water quality are run how many birds flew over and whether the possums cut loose or not,” Mr Walker said.
One of his least favourite types of rainwater piping to tanks was the underground wet-connect method, as it carried real risks if there was a big storm after an extended dry period – all that happens is stagnant water – along with sometimes the aforementioned “raw sewage” – gets washed into the tank.
“We shot ourselves in the foot a little bit by trying to make it all look prettier,” Mr Walker said.
“If you've got one of those wet-connected systems – at the base of the tank, there's usually a screw cap installed on the riser up the face of the tank.
“Consider taking that cap off, strap some mesh or something over the hole, so nothing else crawls in there and dies. But it stops you from catching those summer rain events that just wash the uglies off the roof and spit it in the tank for you.”
He said the conventional method of having a straight downpipe off the roof usually worked safer, and he was also a big fan of concrete tanks, as they kept temperatures down and therefore also the replication rate of bacteria.
Mr Walker added that as rainwater was usually slightly acidic (pH of about 5.5, neutral is 7), concrete tanks fix that because “the acidic rainwater reacts with the cement mix and pulls (a small amount) of calcium out of the wall of the tank” – and the type of roof did make a difference too.
“This passivation also happens on a galvanised iron roof because that's what the zinc's there to do – is to allow itself to be removed to preserve the iron sheeting,” he said.
“That same mechanism means you get a little bit of zinc in your rainwater because that was the price of shifting the pH up a unit or two.
“So if you've got lead flashing and all that sort of thing, then yeah, there's a chance that you'll get a trace of other metals in there as well.
“I can get a tank water sample here, and if I check the pH and it's sitting stupidly low, I can (say) ‘You've got a bloody Colorbond roof and a Colorbond plastic tank, you need to do some remediation of your pH.’”
But he was still happy to see the subject of water quality being raised, as he had certainly collected many testimonials of helping people to track down the cause of sicknesses in not just residents on rural properties but livestock as well.
“There's been a lot of desperate people (saying), ‘I'm spending all this money. I've got all these sheep in containment and lot feeding, and you do the numbers, and I'm spending 10,000 bucks a week on feed, and they put on (only) a gram a day or something. What is going wrong?’
“Every single time, I'm just (saying), ‘give me a water sample.’”
