Rainwater Tank Safety in NZ: Study Reveals Widespread E. coli Contamination

Concerns are mounting around rainwater tank safety in New Zealand after new research revealed widespread contamination in rural drinking water systems, raising serious questions for households relying on roof-collected rainwater.

Major Study Highlights Risks in Rainwater Tank Safety in NZ

A study conducted by scientists at the University of Auckland found that a significant proportion of domestic rainwater tanks across the North Island contained unsafe levels of contamination. The research analysed hundreds of tanks and uncovered that 67% exceeded acceptable E. coli thresholds under New Zealand drinking water standards.

Even more concerning, 86% of samples contained Enterococci, another indicator of faecal contamination. These findings point to systemic vulnerabilities in rainwater collection systems, particularly those that remain untreated and unmonitored.

While metropolitan areas benefit from regulated water infrastructure, more than 15% of New Zealanders rely on self-supplied systems such as rainwater tanks, which often lack oversight.

How Contamination Occurs in Roof-Collected Water

Researchers identified roof catchment systems as the primary entry point for contaminants. Bird droppings, rodents and organic debris accumulate on rooftops before being washed into tanks during rainfall events.

Dan Hawke, co-founder of Forsana, says these findings challenge common assumptions about rainwater purity.

“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.

“More than half (58%) of 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% of tanks also exceeded ammonia guidelines.

“It shows 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,” he says.

Why Maintenance is Critical for Rural Households

The findings reinforce the importance of proactive maintenance for rainwater systems. For many rural and lifestyle property owners, tank water is the primary drinking source, making water quality management a critical responsibility.

“For farmers and lifestyle property owners, managing tank water quality is just as important as maintaining any other part of a property’s infrastructure,” Hawke says.

Guidance from global health authorities such as the World Health Organization supports the need for safe water handling and regular monitoring, particularly in decentralised systems.

Expansion of Water Treatment Solutions Across NZ

The research coincides with Forsana expanding access to its water treatment products nationwide. The company’s hydrogen peroxide-based solutions will soon be available through more than 80 stores operated by Farmlands, as well as additional outlets through Mitre 10.

This expanded distribution is expected to improve access for rural households seeking safer water treatment options.

Hydrogen peroxide has a long history as a disinfectant and is increasingly used in modern applications due to its ability to break down into water and oxygen without leaving harmful residues.

“One of the advantages of hydrogen peroxide is that it does not introduce toxic by-products into water systems or the environment,” Hawke says.

Forsana’s formulation includes ionised silver, designed to stabilise the solution and extend its disinfectant performance.

Growing Demand for Safer Cleaning and Water Solutions

Forsana’s growth reflects broader market trends. The company now operates in more than 600 retail outlets nationwide and has supplied products to over 100,000 customers through its trans-Tasman e-commerce channel.

Demand is expected to continue rising, with global research indicating the natural household cleaners market could reach nearly US$13 billion by 2030.

“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,” Hawke says.

Media Coverage and National Attention

This story has gained traction across national media, including coverage in Otago Daily Times and Newstalk ZB, reflecting growing public concern around rural water safety and environmental health.

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