Tim O'Halloran always thought rainwater from his tank was clean, that was until he put his water supply to the test during a monitoring project.
"You put your rainwater into a little cup, leave it there for an hour or two, then you watch the water turn a horrible, horrible colour and you know it's full of some sort of germs," he said.
The project, conducted at Balranald in the western Riverina, saw 17 water screening tests carried out on rainwater tanks.
Sixty per cent of those returned a positive recording for types of bacteria that could indicate the presence of viral organisms that can make people sick.
Project team member, Charles Sturt University's Peter Waterman, said bacteria readings could be the first sign of other viral organisms being present.
He said filters and chlorine could be used to treat bacteria in water, but there was also an affordable option.
Risks to health
Australian Drinking Water Guidelines suggest the main sources of contamination to rainwater systems are birds, small animals, and debris collected on roofs.
Water sanitation and hygiene consultant Daniel Deere said E. coli and salmonella are most commonly found in tank water, but there are more serious organisms.
"In tropical parts of Australia you can get things like legionella which causes legionnaires disease," Dr Deere said.
Dr Deere said most people can clear microorganisms naturally with no more than mild diarrhoea.
He said vulnerable people were at highest risk of getting ill, while for everyone else it can depend on immunity.
"If you're from an urban centre, or you drink town water, and you go on holiday to a country house somewhere that's got rainwater, it is possible you won't be as immune to what's in that water," Dr Deere said.
Impacts of climate change
A key part of the monitoring project was to determine the impacts of climate change on domestic water supplies in remote and rural areas.
Professor Waterman said some organisms, like Naegleria fowleri, thrive in warmer water.
"It is as happy as Larry to live in water from 23 to over 40 degrees Celsius," he said.
Mr O'Halloran, who lives on a farm in southern New South Wales, said a good way to stay safe was to keep tank surroundings clean.
"You've got to make sure you keep your roof clean so that keeps your rainwater clean," he said.
The national guidelines note that if a system is reasonably well maintained, then rainwater is typically safe to drink.
