Risk Assessment Studies
Numerous international research studies have focused on risk assessments regarding the public health and safety aspects of using alternative circular water for non-potable applications. Below is a brief summary of the conclusions from three relevant and important scientific studies.
The studies were conducted with non-disinfected rainwater or untreated greywater that was artificially highly contaminated
The risk assessment tests demonstrate that the exposure risks associated with this type of use did not lead to unacceptable
If the circular water is additionally treated and disinfected in accordance with EN 16941-1/2 and NSF/ANSI-350, which we strongly recommend, the risk is further substantially reduced.
Practical application and experience with alternative circular water sources for non-potable applications confirm the scientific risk assessment findings. Circular water solutions are already widely deployed, in North America, Europe and other countries and considered practically proven safe technologies.
For more information regarding the three mentioned studies contact us.
"Toilet Use in Relation to Exposure to Microorganisms in Aerosols"
(CTP Publication: 0301, 2003) by C.A.A. Butijn, J.P. Groot-Marcus, W.A.M. Hijnen, M.C. van Putten, P.M.J. Terpstra.
Summary: Toilet flushes with drinking (tap) water were compared to those using raw greywater with a higher dosage of microorganisms. The experiments aimed to quantify how microorganisms are aerosolized from different toilet types and assess the effects of physical contact with lab-simulated greywater compared to tap water. The researchers concluded that the risk of toilet flushing with graywater compared to toilet flushing with potable water, graywater does not cause significant additional health risks compared to toilet flushing with potable water. Most of the risk of exposure to microorganisms in the toilet room is caused by microorganisms in aerosols that come from the standing water (from a previous visit) and not the flushing water.
Since Legionella has not been demonstrated in graywater, the risk of Legionella being atomized during toilet flushes appears to be small, even though laboratory tests show that Legionella does become airborne from the flush water. For now, there are no reasons to believe that graywater causes a substantial risk in toilet flushing compared to drinking water.
"Microbiological Safety of Household Water"
(1999) by G.J. Medema, A. Brouwer, and M. de Graaf.
Summary: This study involved artificially contaminating household (circular) water (representing surface water, rainwater, and raw greywater) with high levels of specific microorganisms for research. These included F-specific RNA phages (MS2 phages) to represent viruses, Clostridium bifermentans spores as a model for persistent pathogens like Cryptosporidium, and Escherichia coli to represent pathogenic bacteria. This highly contaminated water was used in scenarios such as toilet flushing, clothes rinsing/drying, and garden spraying to measure airborne microorganism concentrations. Key observations included:
- Using circular water for toilet flushing didn't significantly increase E.coli and MS2 phages concentrations in the air, though there was a notable increase in spore content.
- Drying clothes in tumble dryers didn't significantly raise the concentration of microorganisms in the air around the dryer or in the condensate collection tray. However, the transfer of microorganisms via hand contact with wet laundry was low but measurable.
- Spraying circular water through a garden hose, particularly with a pressure washer, significantly increased the concentration of all tested microorganisms in the air near the spray.
The study concluded that because contamination levels in real-world untreated household water are expected to be more than 1,000 times lower than those in the study, no measurable increase in airborne microorganisms is expected from toilet flushing, tumble dryers, skin contact with wet laundry, or using a garden hose with a spray head. The exception is the pressure washer, for which even lower contamination levels are needed. The study recommends reducing risk with the pressure washer and using tap water for this application.
“Microbiological and Hygienic Usage Aspects of the use of Rainwater as Process Water for Toilet Flushing, Garden Irrigation, and Laundry Washing”
1996 by R. Holländer", M. Bullermann", C. GroC", H. Hartung", K. König*, F.-K. Lücken, E. Nolde".
Summary: From a total of 102 rainwater storage reservoirs used for toilet flushing, garden irrigation, and, in some cases, laundry washing, approximately 1600 water samples were microbiologically analyzed. The analysis included determining the total number of bacteria at 20 and 37 °C and detecting Escherichia coli, coliform bacteria, fecal streptococci, Pseudomonas aeruginosa, Staphylococcus aureus, Yersinia, Salmonella, Shigella, Legionella, and yeasts. The median value of all total bacterial counts per ml was approximately 1200 (20 °C) and 230 (37 °C), with E. coli at 26 per 100 ml, and coliforms at 198 per 100 ml. The values in plastic tanks were lower than those in concrete and brick tanks. Except for the ubiquitous Pseudomonas aeruginosa (detected in 11.8% of the samples) and Salmonella in one sample, no pathogenic bacteria were detected. Compared to the limits for swimming water (EU standard), more than 95% of all analyzed samples met these requirements. With precautions such as strict separation of the drinking and rainwater pipe networks, labeling of the pipe network and tapping points, rainwater collected in rainwater tanks poses no hygienic risk when used as operational water in households (toilet flushing, laundry washing, garden irrigation).