Industry experts have been calling for greater awareness of rainwater tank safety after new research found two-thirds of tanks tested exceeded acceptable levels of E. coli.
While New Zealand reports universal access to safely managed drinking water supplies in metro areas, more than 15 percent of the population relies on domestic self-supplied systems such as roof-harvested rainwater tanks, which are typically unmonitored and untreated.
The new study by University of Auckland scientists analysed hundreds of rainwater tanks across the North Island and found widespread contamination in domestic roof-collected water supplies.
The majority of tanks exceeded acceptable levels of E. coli under New Zealand drinking water standards, while 86 percent exceeded acceptable levels of Enterococci, another indicator of faecal contamination.
Researchers said contaminants typically enter tanks through roof catchment systems, where bird droppings, rodents and organic debris accumulate before being washed into storage tanks during rainfall.
Dan Hawke, co-founder of Christchurch-based Forsana, which manufactures environmentally friendly cleaning and water treatment products, said the findings highlight how vulnerable roof-collected rainwater systems can be if tanks are not properly maintained and show the urgent need for greater awareness of rainwater tank safety and treatment, particularly in rural areas.
“The fact that most tanks tested exceeded acceptable E. coli levels is a clear reminder that untreated rainwater is not always as clean as people assume. In addition to microbial contamination, the study found a range of other water quality issues," he said.
“More than half of the tanks failed recommended pH standards, a small proportion exceeded turbidity limits, and all samples showed elevated water hardness. In regions like Taranaki, more than 60 percent of tanks also exceeded ammonia guidelines."
Hawke added that while rainwater is often assumed to be clean, in reality, these systems can be exposed to a range of environmental contaminants if tanks are not regularly maintained or treated.
In rural areas, many households rely entirely on rainwater tanks for drinking water, and because those systems collect water directly from roofs, they can easily pick up contamination from bird droppings, rodents and organic debris.
The findings also reinforced the importance of regular tank maintenance and treatment. For farmers and lifestyle property owners, managing tank water quality is just as important as maintaining any other part of a property’s infrastructure.
The research came as Forsana expanded distribution of its hydrogen peroxide-based products through rural retail networks, improving access for farmers and lifestyle property owners who rely on rainwater tanks.
Hydrogen peroxide has been used for more than two centuries and was widely deployed as a disinfectant during the World Wars. Today, it is increasingly used in household cleaning, water purification and plant care applications.
Hawke said the compound offers a safer, environmentally friendly cleaning and disinfecting option because it breaks down into water and oxygen, leaving no harmful chemical residues.
One of the advantages of hydrogen peroxide is that it does not introduce toxic by-products into water systems or the environment.
He added that tightening environmental regulations has contributed to the shift towards safer cleaning products.
“We are seeing increasing restrictions on chemicals such as phosphates and other substances that can harm waterways and ecosystems, which is encouraging manufacturers and consumers to look for safer alternatives.”
Forsana is currently working through Australia’s regulatory approval process, which requires additional registrations before products can be marketed as disinfectants.
In New Zealand, the formulation is approved as a hospital-grade disinfectant and is used across a range of sectors, including health care, commercial plant care, vehicle rentals, and the domestic market.
