COVID-19 and Recycled Wastewater Irrigation: A Review of Implications

This (non-peer reviewed) preprint is a collaborative study between researchers in Australia and Bangladesh. It considered the use of reclaimed wastewater for irrigation. While this is a very different application to the use of purified recycled water for supplementing drinking water supplies, the authors appear to have drawn very different conclusions to those described in an editorial perspective that we wrote about earlier today.

In the abstract of this preprint, the authors state that “the novel SARS-CoV-2 is now perceived as an enteric pathogen, and has been found to remain stable in the wastewater for days”. In our opinion, neither of those two statements is accurate. SARS-CoV-2 is generally not perceived to be an enteric pathogen since no evidence of faecal-oral transmission has been reported. Furthermore, there is no direct evidence that SARS-CoV-2 virions remain stable and viable in wastewater for a period of days.

The authors follow this statement with the following:

Mounting evidences also suggest that viral particles shed by infected individuals through sewage, and greywater is much higher (up to 10 Log10) than the amount typically removed (6-7 Log10) through the recycled water disinfection processes. Such gap indicated an increased risk of infection through fecal-oral transmission route”.

However, this appears to be based in a misunderstanding of the current literature regarding SARS-CoV-2 in sewage. Around a dozen papers have reported the detection of fragments of SARS-CoV-2 RNA in sewage, mostly with the intention of establishing wastewater-based epidemiology for COVID-19 (see our list at start of this recent blog post). But it is wrong to assume that the presence of SARS-CoV-2 RNA implies the presence of viable infectious virions. Therefore, there is currently no basis on which to assume that high concentrations of infectious SARS-CoV-2 exist in sewage, and there is growing evidence to indicate that they most likely don’t.

Based on similar failures to differentiate between SARS-CoV-2 RNA and infectious virions, this study also proposed that greywater irrigation schemes pose an unsafe risk of transmission of SARS-CoV-2. It was recommended that “countries putting greywater in the ‘low risk’ category may rewrite the safety guidelines in post COVID-19 times”.

There are certainly some valid concerns to be raised regarding potential exposure to community members via contaminated water sources such as sewage and greywater. And in the absence of complete information, it is appropriate that precautionary measures be taken. However, this paper does not present an appropriately balanced appraisal of risks, according to current knowledge and reasonable extrapolations of that knowledge. As such, we would strongly recommend that the paper not be accepted for publication in its current form.


Oliver, M.M.H.; Hewa, G.A.; Pezzaniti, D.; Haque, M.A.; Haque, S.; Haque, M.M.; Moniruzzaman, M.; Rahman, M.M.; Saha, K.K.; Kadir, M.N. COVID-19 and Recycled Wastewater Irrigation: A Review of Implications. Preprints 2020, 2020060105.

Published by Stuart Khan

Professor of Civil & Environmental Engineering, University of New South Wales

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