Rainwater Harvesting Myths

There are a series of myths about rainwater harvesting that do the rounds and get recycled every couple of years. We thought it might save time if we listed them here and provided  a response.

Rainwater Harvesting doesnt provide enough water to be considered in water policy

  • 1.7 million households, over 5 million Australians, own a rainwater tank.
  • Rainwater represents 8% of household water use nationally.
  • The value of rainwater in 2013/14 was $507 million nationally.
  • Rainwater Harvesting provided more  water than desalination plants in 2012
  • Rainwater is a major source of water in Australia

Source ABS 2015

Rainwater Harvesting costs more than  Mains Water

ABS water account household expenditure

ABS water account household expenditure

Well, rainwater must be getting more expensive pretty fast, household water bills has increased by 91% for major water utilities since 2008.

The average 5000 litre rainwater harvesting system costs about $3000 and should last 20 years. Rainwater  harvesting and water efficient appliances save about 90kl (a kilolitre is 1000 litres) each year. Based on those figures rainwater harvesting is costing around $2.00/kl.  The calculation includes an allowance for water efficient appliances, pump replacement and electricity charges. Most people pay more than $2.00 for potable water plus charges of over $100/quarter.

However, there is a very interesting side to this discussion. Systems modelling by Professor Coombes shows that a combined system relying on rainwater harvesting first and then potable water would save both householders and water utilities billions of dollars in avoided water infrastructure and operational costs.

Major water utility Operational costs

Major water utility Operational costs


NSW Major utilities were the most expensive to operate in Australia in 2008.

BASIX was introduced in 2004 including rainwater harvesting and water efficient appliances and water saving targets.

NSW major utilities now have half the operational costs/property as QLD utilities and our seriously outperforming all the other major water utilities in the country.

Rainwater Harvesting doesn’t work because in a drought it doesn’t rain

Rainfall during the millenium drought in Brisbane

Rainfall during the millenium drought in Brisbane

Wrong. Rainfall records for every capital city show that reliable rainfall through the last drought kept on providing a source of water when traditional dams  had almost disappeared.





Rainwater harvesting doesn’t really change the stormwater profile

Integrated stormwater benefits

Integrated stormwater benefits

Putting a rainwater tank on each house has multiple physical and ecosystem responses in catchments.

Distributed top of catchment and in catchment solutions at multiple scales, single household, neighbourhood, suburb and regional cumulatively reducing stormwater volumes and delaying peak flows, substantially reducing treatment costs  and flooding risks.

The Queensland Government showed Rainwater Harvesting is not cost effective

The 2012 Queensland Competition Authority cost-benefit report made a small assumption, in the modelling for rainwater harvesting all pumps would fail after 10 years and 0% of them would be replaced. All rainwater harvesting systems supported by government policy would cease to operate 10 years after installation.

SEQ rainwater harvesting yield

SEQ rainwater harvesting yield

—As a result water savings were underestimated by 90%, as were operational savings of $3.5B.

—The Coombes/RHAA estimate of the benefit cost ratio is 2.1:1.

These findings are published in the Australian Journal of Water Resources and have been peer reviewed.

There are serious health risks associated with drinking rainwater

Over 2.3 million Australians drink rainwater every day, Australia is the largest case study in the world for safe rainwater drinking.

EnHealth Australia has this to say on the subject

The general public perception is that rainwater is safe to drink. In most areas of Australia, the risk of illness arising from consumption is low, providing it is visually clear, has little taste or smell and, importantly, the storage and collection of rainwater is via a well maintained tank and roof catchment system. While the risk from consuming rainwater is low in most areas of Australia, the water from domestic tanks is not as well treated or managed as the major urban water supplies. The microbial quality of water collected in tanks is not as good as that in urban supplies. In a limited number of areas, specific industries or very heavy traffic emissions may affect the chemical quality of rainwater.

Enhealth go on to say that if mains water is available than it  is better quality than rainwater and should be used in preference, not that it will make you ill. People who drink rainwater appear to have the same health levels as the general population, there are over 20 years of reports on this topic.

People who drink rainwater appear to have the same health levels as the general population, there are over 20 years of reports on this topic.

  • Heyworth et al. – The risk of attaining “highly credible gastrointestinal symptoms” (HCG) in 4-6 year old children was significantly less among children drinking rainwater alone, compared with drinking chlorinated & filtered public mains water.
  • Rodrigo et al. – The risk of HCG was not appreciable for households drinking untreated rainwater compared to treated rainwater.

Some studies say there is evidence of cryptosporidium or giardia or similar in rainwater, particularly the gutters. These studies are careful not to say that people are actually getting sick.

There is good evidence for a natural treatment train in rainwater tanks that reduces the risk of infection and health risks affecting human drinkers. That doesn’t mean that you cant get sick from rainwater, but you won’t find the experts telling you won’t ever get sick from mains water either.