In Australia, there is a debate on the health of people using harvested rainwater. Earlier this year (2016), at the Rainwater Harvesting Association of Australia (RHAA) seminar in Sydney, a presentation that included recent research by PJ Coombes of Urban Water Cycle Solutions was presented. This article will explore some of the issues presented and the different sides.
Sources of Information
It is critical to appreciate the potential biases of people who engage in any argument. For example, much commentary on the healthiness of using harvested rainwater according to Smit and Coombes is “funded by water monopolies who have a centralised water distribution perspective quite different to how rainwater harvesting works.”
Evidently, water monopolies who control a centralised water supply stand to lose money if everyone began becoming self-sufficient and depending upon their rainwater. Thankfully, while their voice is influential, there exist wide differences of opinion on the safety of rainwater use.
RHAA and PJ Coombes come from the other side, based upon empirical studies and research, support the safety of rainwater use as long as simply measures are taken to avoid water contamination.
Real-World Evidence for Rainwater Safety
Rainwater has been depended upon out in the country as a primary source of high-quality water for some time. In fact, the widespread use of rainwater and the absence of health epidemics makes a quite compelling case for its safety. As noted in the article, Rainwater Health Debate:
Australia has a substantial real world case study with over 2.3 million Australians relying on rainwater for drinking water and more than 6.3 million people using rainwater for some household use. In spite of claims of widespread health concerns, there are no health epidemics or widespread notifications of lead contamination by chief medical officers.
Two Concerns with Rainwater Use
There are two main issue often presented against the safety of consumption of rainwater in harvested in water tanks:
- Lead contamination – the influence of roofing material and lead flashing contaminating rainwater tank with poisonous metals.
- Sludge and biofilm contamination – even with water diverters and strainers installed, over time particle still find their way into a tank. This turns into a layer of sludge which reportedly causes contamination and can be a breeding ground for harmful bacteria.
A publication by Magyar et al (2014), Influence of roofing material and lead flashing on rainwater tank contamination by metals, argued that there was widespread lead contamination in rainwater harvested in tanks.
All sides are in agreement that lead flashings, which stop water penetrating the junction of a roof, should be avoided. There is very good evidence that lead flashing is damaging to rainwater quality and so should be avoided if collect rainwater for consumption.
Thankfully, building controls in place before the research was carried out address these concerns. Still, many home owners may not be sufficiently aware that lead was once used in flashings in time past. Where lead flashing is on a roof that collects rainwater for drinking purposes, then it should be removed as a priority.
On the other hand, the proposition is that there are high levels of lead in rainwater tanks without lead flashing, such requires further evidence and discussion.
Sludge and Biofilm Contamination
The sludge layer that forms at the bottom of a rainwater tank is frequently regarded as a contaminant source (e.g., Magyar and Ladson). Others, such as Coombes and Spinks, consider sludge as a useful tool for purifying rainwater and preserving its quality.
According to certain research, lead contamination may be found in 23% of urban rainwater tanks; nevertheless, as previously said, we must ask why there aren’t more widespread reports of lead poisoning among the 2.3 million Australians who drink rainwater.
Coombes’ own investigation into ancient inner-city homes in industrial regions contradicts this study, finding no substantial lead exposure. In reality, over a thousand tanks in various regions of Australia were studied during the last 15 years, and just a few of them were found to be contaminated with lead. Why? According to Coombes and Smit:
The rainwater treatment train, which encompasses the natural processes of flocculation, settling, biofilms (including sludge), and competitive exclusion of bacteria, has been confirmed by a decade of independent study (where more resilient environmental bacteria eliminate more fragile potential pathogens).
Coombes’ own investigation into ancient inner-city homes in industrial regions contradicts this data, finding no substantial lead exposure. In reality, over a thousand tanks in several regions of Australia were tested for lead pollution during the last 15 years, and only a small percentage of them were found to be contaminated. Why? Coombes and Smit make the following point:
The rainwater treatment train, which includes natural processes such as flocculation, settling, biofilms (including sludge), and competitive exclusion of bacteria, has been confirmed by a decade of independent study (where more resilient environmental bacteria eliminate more fragile potential pathogens).
There is not the presence of a thick green or black slime that smells that one would normally associate with a pond. Some very poorly maintained rainwater tanks may reach such a state, but a fully operating rainwater harvesting system with water diverters and strainers as found in urban areas are unlikely to display such characteristics.
Conclusion on Rainwater Safety
Ironically, the assumption that the quality of rainwater is poor because of sludge appears to be turned on its head if this biofilm acts as a kind of “sticky filter” that absorbs otherwise heavy contaminants and metals like lead. Despite disagreements, all agree there is a real benefit to be had in ensuring the design, maintenance and management of rainwater harvesting systems with adequate protocols developed based upon evidence.