Yes, we believe that when good design and sensible maintenance practices, as outlined in our book, are employed, that rainwater is safe and does not pose a health risk. It does not necessarily need to be sterilized or disinfected prior to it’s use.
However, there is definitively a difference in opinion.
We’ve highlighted some of the discussion below and point you to the following summary blog, Rainwater Health Debate, as well as point to peer-reviewed published papers.
Top of page:
The Coombes presentation at the RHAA seminar in Sydney about widespread use of rainwater and the absence of health epidemics is compelling. 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.
Mid Page:
The discussion also highlights an interesting point about sludge. On the one hand Ladson and Magyar see sludge as a source of contamination whereas Spinks and Coombes see sludge as a key part of the treatment train protecting rainwater quality. A decade of independent research has discovered and confirmed the rainwater treatment train that includes the natural processes of flocculation, settlement, biofilms (including the sludge) and competitive exclusion of bacteria (where more resilient environmental bacteria eliminate more fragile potential pathogens). So is the quality of rainwater poor because lead and other contaminants might be found in the biofilm layer known as sludge? The answer is no because the biofilm is highly effective at removing lead and other contaminants from the water column. This research highlights that the sludge layer is held together by sticky polysaccharides common to biofilms and it should not be disturbed by regular cleaning (for example). The use of leaf diverters and mesh screens improves this natural treatment train by excluding sediments and debris from the storage.
Bottom of the page:
There are three interesting points about sampling The original Ladson and Magyar publication noted that rainwater tank water was taken from the tap on the tank and this is a key point. But results for rainwater quality will be different at different points on the rainwater harvesting process, from gutter, to tank, to tap. Sampling at the gutter or at the water surface in a tank is almost meaningless in this context as that is not what people are drinking and there is a treatment train occurring within the rain harvesting system. Again, applying a similar logic to mains water supplies and basing assumptions about water quality on inflows to dams could result in closure of mains water supplies for assumed health reasons. Secondly the use of Polymerase Chain Reaction analysis must be verified by independent testing as Coombes found it to be highly vulnerable to sampling and interpretation errors. Thirdly sampling should be consistent with final use, it is disingenuous for example to sample a disused garden rainwater tank and then apply those results to assumptions about drinking water health.
Coombes, P.J. 2016. “Response to Reply by AR Ladson and MI Magyar,” in Vol 19, No.1, pp. 88–90, Australian Journal of Water Resources, DOI. Available online: http://dx.doi.org/10.1080/13241583.2015.1131597
Page 2, on using e.Coli as an indicator of water quality:
Use of e. coli as an indicator of possible faecal contamination of environmental waters is likely to result in overestimation of perceived risk.
Page 2:
Our research has revealed a rainwater treatment train (for example: Coombes 2002; Spinks 2007; Morrow 2012) and has confirmed that the quality of rainwater varies at divergent points in the rainwater harvesting systems from roof to storage to tap (for example: Morrow 2012, Morrow et al. 2010; Evans 2010; Martin et al. 2010; Spinks 2007, Coombes 2002). The assessment of water quality from rainwater harvesting systems is critically dependent on the sample location within the treatment train, position in the rainwater storage and on repeated sampling protocols. It was a key finnding by Morrow (2012) and Coombes (2002) that that the general nature of rainwater sampling investigations obscures actual water quality outcomes.
Coombes, P.J. 2015. Discussion on “Influence of Roofing Materials and Lead Flashing on Rainwater Tank Contamination by Metals,” by M.I. Magyar, A.R. Ladson, C. Daipe, and V.G. Mitchell. Australian Journal of Water Resources 19(1).
Abbott, S., Caughley, B. 2012. “Roof-Collected Rainwater Consumption and Health.” Paper presented at the 5th Pacific Water Conference. Nov 1, 2012. Auckland, NZ. Available online: http://www.pwwa.ws/pdfs/Stan_Abbott_RWH_Consumption_Health_Handout.pdf.
Page 10.
Because of the many benefits roof water harvesting should unquestionably be encouraged for both urban and rural environments since rainwater tanks are a visible and high profile method of conserving water and can be used to reinforce and promote water conservation policies and practices. However, there must be an awareness among the general public, local authorities, and regional public health services about the health risks associated with contaminated roof water. Providing the roof-collected rainwater is clear, has little taste or smell and is collected from a well-maintained system, it is probably safe and unlikely to cause any illness in most users. The health risks of roof- collected rainwater can be minimised by sensible preventative management procedures. Some of the preventative measures are associated with design and installation while others are associated with ongoing maintenance. Well-designed systems are low maintenance and will generally prevent problems occurring so that corrective action to restore safe rainwater quality will be needed infrequently.
Dean, J. and Hunter, P.R. 2012. “Risk of Gastrointestinal Illness Associated with the Consumption of Rainwater: A Systematic Review.” Environmental Science and Technology 46, pp. 2501–2507. Available Online: https://pubs.acs.org/doi/abs/10.1021/es203351n
We conclude that the evidence suggests that rainwater is safer than water from unimproved water supplies. Where feasible rainwater harvesting should be encouraged as a step toward achieving millennium development targets.
enHealth. 2010. “Guidance on the Use of Rainwater Tanks,” 3rd Ed. Commonwealth of Australia. Available online: http://www.health.gov.au/internet/main/publishing.nsf/Content/ohp-enhealth-raintank-cnt.htm
Pg iii:
Collection and storage of rainwater involves relatively simple systems. A reasonably low level of management can ensure provision of good quality water that can be used for a wide range of purposes including drinking, food preparation, bathing, laundry, toilet flushing and garden watering.
Pg 9, on Legionella:
While rainwater tanks can provide environments for Legionella, they are common environmental organisms. Infection normally follows amplification in warm water and dissemination in aerosols. There is little evidence that rainwater tank supplies are associated with increased public health risk. Tanks should be kept clean and the rainwater, when used in hot water systems, stored and delivered to reduce the likelihood of the growth of Legionella bacteria, and also reduce the likelihood of burns and scalds.
Pg 9, on illness and rainwater tanks:
The relatively frequent detection of faecal indicator bacteria is not surprising, given that roof catchments and guttering are subject to contamination by bird and small animal droppings. However, despite the prevalence of indicator organisms, reports of illness associated with rainwater tanks are relatively infrequent. Although traditional under-reporting of gastrointestinal illness will contribute to a lack of evidence, epidemiological investigations undertaken in South Australia have failed to identify links between rainwater tanks and illness (Heyworth et al. 1999; Heyworth 2001; Rodrigo et al. 2010).
Pg 10, on illness and rainwater tanks:
In summary, the study conducted in South Australia found no measurable difference in rates of gastrointestinal illness in children who drank rainwater compared to those who drank mains water. However, there are examples of Campylobacter and Salmonella enteritis associated with rainwater tanks and one example of cryptosporidiosis/ giardiasis associated with an underground tank. Faults in tank design or poor maintenance were identified as contributory factors in some of the investigations of illness.
P. 26, on testing:
Microbial testing of rainwater from domestic tanks is rarely necessary and in most cases is not recommended. Water quality in rainwater tanks can change rapidly during wet weather and, during dry periods, the concentrations of indicator bacteria (E. coli) and faecal pathogen numbers decrease due to die-off (Edberg et al. 2000). Testing for speci c pathogens is often expensive and is generally only warranted as part of an outbreak investigation. If there are strong concerns about water quality, chlorination of tank water is a suitable alternative to testing. If microbial testing is undertaken, the parameter of choice is E. coli as an indicator of faecal contamination. Tests for total coliforms or heterotrophic plate counts are of little value as indicators of the safety of rainwater for drinking.
Chemical testing should only be required in exceptional circumstances, such as in specific areas where there are concerns about impacts from major industrial or agricultural emissions. In these circumstances the chemicals of concern need to be identifed before testing or large costs can be incurred with limited likelihood of successful detection.
