Considerations for Large Building Water Quality after Extended Stagnation

Most of the world’s cities have been under some form of lock-down during the first few months of the global COVID-19 crisis. This means that many large (and small) buildings have been sparsely inhabited for periods of weeks or months. In many cases, drinking water supplies to those buildings will be lying dormant in pipes and storage tanks. This raises some important questions:

  • How might this affect water quality?
  • What are the public health risks?
  • How should building water supplies be managed during sparse population?
  • How should water supplies be re-commissioned as buildings are gradually repopulated?
  • What guidance is available for building managers and others to follow?

These questions are addressed in a forthcoming paper (currently available as a non-peer reviewed pre-print) titled “Considerations for Large Building Water Quality after Extended Stagnation”. This work was undertaken by a group of water quality researchers in the US and Canada, led by Prof Andrew Whelton at Purdue University.

The paper presents a synthesis of peer-reviewed, government, industry, and nonprofit literature relevant to the implications of water stagnation in plumbing systems and decontamination practices for water quality and health. Key concerns identified include:

A range of water management practices are canvassed for managing these potential impacts to water quality and public health for sparsely populated buildings. These include periodic flushing and, where water quality can’t be otherwise managed, full building closures.

Important considerations for building recommissioning (following a period of sparse occupation) are also provided. Possible actions include system flushing and the use of shock-disinfection. The importance of effective risk communication is also discussed.

A YouTube video describing this study is available at

The International Water Association (IWA) COVID-19 Task Force is currently planning a webinar panel to explore these issues further and provide the opportunity for questions. Keep an eye on this COVID-19 Waterblog for upcoming details.


Proctor, Caitlin, William Rhoads, Tim Keane, Maryam Salehi, Kerry Hamilton, Kelsey J. Pieper, David M. Cwiertny, et al. 2020. “Considerations for Large Building Water Quality After Extended Stagnation.” OSF Preprints. April 8.

Purdue engineering professor Andrew Whelton holds up a water sample from a building faucet. The pink color indicates the presence of chlorine, a disinfectant. Whelton’s team is investigating how water quality might change in buildings during a time of limited occupancy due to the COVID-19 pandemic. (Purdue University photo/Matthew Kerkhoff) 

SARS-CoV-2 in wastewater: State of the knowledge and research needs

This paper presents a review of the current research outcomes and needs regarding SARS-CoV-2 in wastewater. The fact that such a review should exist so soon after the presence of this virus in wastewater became an issue of interest seems remarkable. But it is also a clear reflection of the avalanche of research on this topic, which is still only in its first few rumblings.

The authors of this paper include researchers with long and distinguished careers in developing the science around viruses in water and wastewater (Charles Gerba, Annalaura Carducci and Joan Rose), teamed with some younger scientists all now right at the forefront of this field internationally (Masaaki Kitajima, Warish Ahmed, Kerry Hamilton, Eiji Haramoto and Kyle Bibby). So this review and its conclusions can be considered to be very well informed.

The review does provide an update and guidance on “wastewater-based epidemiology” from the presence of SARS-CoV-2 genetic material (RNA) in sewage. This topic has also been covered fairly extensively on this blog (select “wastewater-based epidemiology” from the “Tags” at the bottom of any of our blog pages to find examples).

More unique about this review is the effort to pull together the key information that will be required for assessing public health risks associated with the presence of viable SARS-CoV-2 virus in wastewater and drinking water.

These include attention to the survival and inactivation of coronaviruses and enveloped surrogate viruses in water and wastewater matrices. The authors also describe the data needs (and data availability) for quantitative microbial risk assessment (QMRA) for COVID-19. These include the need for dose-response data for SARS-CoV-2, for which they identify none as currently available (and maybe SARS-CoV might be the currently best available surrogate).

While the paper did include a passing mention of the important WHO metric “Disability Adjusted Life Years” (DALYs), the authors did not identify the establishment of a “DALYs-per-case” value for COVID-19 as among the current knowledge gaps and research needs. Nonetheless, such a value will be required in order to establish safe levels of drinking water management by current WHO (and Australian) procedures. It will also be neccesary to develop a quantitative understanding of the performance of various water treatment processes for removing or inactivating the virus.

The concluding remarks from this review include a call for more information and understanding to be developed as a matter of urgency:

Our understanding on the potential role of wastewater in SARS–CoV-2 transmission is largely limited by knowledge gaps in its occurrence and survival in wastewater and environmental waters and removal by wastewater treatment processes. There is an urgent need for collecting these pieces of information to understand and mitigate the human health risks associated with exposure to wastewater and environmental waters potentially contaminated with SARS-CoV-2”.


M. Kitajima, W. Ahmed, K. Bibby, et al., SARS-CoV-2 in wastewater: State of the knowledge and research needs, Science of the Total Environment (2020).

SARS-CoV-2 known and unknowns, implications for the water sector and wastewater-based epidemiology to support national responses worldwide: early review of global experiences with the COVID-19 pandemic

As many people would have observed, there is currently a large amount of work being undertaken internationally in support of wastewater-based epidemiology for COVID-19. That is, searching for fragments of genetic material (RNA) from the virus SARS-CoV-2 in sewage (or sludge from sewage treatment plants), with the aim of understanding patterns of infection within communities.

We listed and provided links to nine recent papers on our previous post, here. Reading through these studies, it is clear that there are currently some very big methodological variations among them. For example, there are major variations in sample collection, RNA concentration and extraction, which fragments of RNA to target, quality control procedures, and how to quantitatively interpret the results.

This variability may be helpful in that it means that many diverse approaches are being trialled, which may lead to identification of the optimum approaches. But it also means that it is practically impossible to directly compare the reported results between different cities due to the number of potentially confounding factors that need to be considered.

So it is timely that we begin to see some key papers identifying the need for a more coordinated way forward. This paper, led by researchers at Water Research Australia (WaterRA) provides an important step in that direction.

As each new pre-print reporting wastewater-based epidemiology of COVID-19 is produced, it is accompanied by a flurry of excitement, both in conventional media and on social media. However, the authors of this paper remind us that there is still some way to go with developing the true usefulness of these techniques:

Currently, there is limited quantitative data on the intensity and duration of shedding of the SARS-CoV-2 virus in faeces and respiratory fluids over the course of infection, and there is no simple way to equate a measure of virions/L of wastewater to the number of infected people in the wastewater catchment from which the wastewater is collected. Therefore, it is important to appreciate that it is uncertain how useful such testing will be in providing information to those tasked with managing the COVID-19 pandemic response”.

Nonetheless, progress is being made and the authors report some major efforts underway to improve coordination and networks among key researchers and other organisations. These include networks in Australia (through Water Research Australia), Canada (Canadian Water Network) and the US/globally (Water Research Foundation).

Beyond the many technical issues requiring further development, the authors describe how there are also important communication challenges requiring attention. These include explaining and communicating that there is no evidence that infectious SARS-CoV-2 virus is transmitted through wastewater. Another need is communicating the costs, value and benefits of environmental surveillance to agencies leading the COVID-19 control strategies. That means communicating the differences and alignments between clinical and environmental surveillance and how the two are complementary.


Hill, K., Zamyadi, A., Deere, D., Vanrolleghem, P. A. and Crosbie, N. (2020) SARS-CoV-2 known and unknowns, implications for the water sector and wastewater-based epidemiology to support national responses worldwide: early review of global experiences with the COVID-19 pandemic. Water Quality Research Journal.

Can we estimate the Disability Adjusted Life-Years (DALYs) for COVID-19 yet?

Many water quality guidelines now use Disability Adjusted Life-Years (DALYs) to define a tolerable level of risk for pathogenic substances in drinking water. Examples include the WHO Guidelines for Drinking-water Quality, WHO Potable Reuse Guidelines and Australian Guidelines for Water Recycling.

Any supply of drinking water carries risks of exposure to pathogenic organisms (viruses, bacteria, protozoa). Those risks might be very small, but they never actually reach ‘zero’ since its impossible to absolutely guarantee that nothing will go wrong ever. If we accept that, then its very helpful to quantitatively define a tolerable level of risk so that we can design our water supplies to meet that level.

In each of the above cases, the tolerable level of risk (for each pathogen) has been defined as that which corresponds to a loss of 10-6 DALYS per person per year. This level is often referred to a 1 microDALY per person per year.

In order to define a suitable level of risk management (usually water treatment) against pathogens, we need to know a number of things, but key among them is the number of DALYs associated with each (risk of) infection. That is, the number of DALYs per case.

Some important examples are included in the WHO Guidelines for Drinking-water quality (See Chapter  7 “Microbial Aspects”). These are:

  • Cryptosporidium: 1.5 × 10−3 DALYs per case
  • Campylobacter: 4.6 × 10−3 DALYs per case
  • Rotavirus: 1.4 × 10−2 DALYs per case

If we want to know whether drinking water is being protected to the same burden of disease risk for SARS-CoV-2 as for these three pathogens, we need a DALYs per case value for SARS-CoV-2. This is a problem for newly important pathogens, since an official DALYs per case value may take years to be produced. So, in the meantime, can we estimate the number of DALYs per case for SARS-CoV-2?

I’m going to give it a go, but I’ll be grateful for your feedback and suggestions for improvement.

As a starting point, I took this paper, recently published in Science, titled “Estimating the burden of SARS-CoV-2 in France”. France seems like a good place to acquire these data from since they had high numbers of infection (more than Australia) and a good public health system with effective reporting.

This paper reports the following statistics:

  • Rate of hospitalisation among infected persons
  • Rate of intensive care admission among hospitalised cases
  • Rate of death among hospitalised cases.

From the first of these, it is also simple to derive:

  • Rate of non-hospitalisation among infected persons

Since the rate of various outcomes are age-dependant, the data for these statistics are broken into age categories (<20, 20-29, 30-39, 40-49, 50-59, 60-69, 70-79 and 80+).

The number of DALYs attributed to infection is determined by the range of debilitative outcomes (including their severity and duration) and the number of deaths (and their associated expected life years lost).

The severities for various debilitating outcomes are defined in terms of “Disability Weights”. A large database of Disability Weights is available from the Global Health Data Exchange. Some more information on how these numbers are derived (and what they actually mean) is available from this paper on “Assessing disability weights based on responses from 30,660 people from four European Countries”.

Searching through these disability weights, the following appear to be reasonably good matches for the likely range and severity of illnesses from COVID-19. Its important to remember that these are “average” severities, thus many people could experience greater severities and the numbers will be balanced by people who experience lesser severities:

Non-hospitalised COVID-19 cases: Roughly consistent with the sequela “Moderate lower respiratory infections”. This has the health state name “Infectious disease, acute episode, moderate” and the lay-person description of “has a fever and aches, and feels weak, which causes some difficulty with daily activities”. The Disability Weight for this condition is 0.051 (0.032-0.074).

Hospitalised COVID-19 cases: Roughly consistent with the sequela “Severe lower respiratory infections”. This has the health state name “Infectious disease, acute episode, severe” and the lay-person description of “has a high fever and pain, and feels very weak, which causes great difficulty with daily activities”. The Disability Weight for this condition is 0.133 (0.088-0.190).

Intensive Care Unit COVID-19 cases: For this state, the highest Disability Weight available in the Global Health Data Exchange database has been applied. This is for the unrelated condition “Schizophrenia acute state” with the lay person description of “hears and sees things that are not real and is afraid, confused, and sometimes violent. The person has great difficulty with communication and daily activities, and sometimes wants to harm or kill himself (or herself)”. The Disability Weight for this condition is 0.778 (0.606-0.900). Although this may not seem like a perfect fit, we will see that the sensitivity of the final result to the selection of this number is low.

Deaths of COVID-19 cases: The statistic that is available is the “rate of death among hospitalised cases”, which may not fully capture the overall rate of death among COVID-19 infections. However, in this case, we will make an assumption that most deaths applied to hospitalised cases. DALYS for deaths are determined according to the number of life-years lost, which is a function of age and (age-specific) average life expectancy. The weighting factor in this case is 1 (per year).

Duration of illnesses

All living conditions (non-hospitalised COVID-19 cases, hospitalised COVID-19 cases, and Intensive Care COVID-19 cases) have currently been estimated to have a duration of 10 days. It is expected that these could be updated with more precise data. However, sensitivity testing indicates that the final result is not highly sensitive to these numbers. The hospitalised and ICU durations can each be increased up to 100 days without significantly changing the final result. The “not hospitalised” case durations can be increased to around 30 days before they start to have a significant impact on the result.

Age proportion of the population

Given that the burden of disease data are available in age-categories, it is necessary to estimate the proportion of the population that each age-category applies to. This figure will vary somewhat among different populations, but in this case, data from Australia has been applied.

Data were obtained from the Australian Bureau of Statistics for “Estimated Resident Population By Single Year Of Age, Australia”. Data were used from June 2019, which included population numbers for each year of age, from “0” to “100 and over”.  From this, the following population percentages were derived:

  • Age <20: 24.6%
  • Age 20-29: 14.5%
  • Age 30-39: 14.5%
  • Age 40-49: 12.9%
  • Age 50-59: 12.1%
  • Age 60-69: 10.3%
  • Age 70-79: 7.1%
  • Age 80+: 4.0%

Age-specific life expectancy

Average life-expectancy in Australia is, itself an age-specific value. That’s because as a person ages, they pass the risk of childhood and adolescent deaths.

Age-specific life expectancy was derived from data (for 2016-18) published by the Australian Bureau of Statistics. Life expectancies differ for males and females, so an average value was taken for each age year. Then a weighted average life expectancy was calculated for each of the above age categories, according to the portion of people in each year age group. These gave average life expectancies of 74 years (remaining) for people aged <20 and average life expectancies of 7 years (remaining) for people aged 80+. The calculated average life expectancies for all of the age categories are shown in the tables below as “Life Years Lost”.

Calculation of DALYS for each of the three health states and deaths

The (weighted) average number of DALYs lost for each of the three health states and deaths is presented in the following four tables. Quick inspection of these numbers reveals that a final sum derived by the combination of all four states will be dominated by the DALYS for “deaths”. And the DALYS for “deaths” figure is, itself, dominated by the life years lost by people aged 60 and above.

This explains why most of the figures applied in the calculations for the three (non-death) health states (eg, Disability Weights and illness durations) are not shown to have a high sensitivity on the final calculated result.

Final calculated DALYS per case of COVID-19.

The final numbers of DALYs per case of COVID-19 is calculated as the sum of the DALYS derived four each of the four states. The sum is 0.088 DALYs per case (but see update in “Addendum” below). This is a large number, -much bigger than the numbers given at the start of this blog post for common waterborne pathogens. This reinforces the fact that it is appropriate to make great efforts to prevent people being infected with this virus.


There are many uncertainties with this calculation, some of which have already been described above. Uncertainties associated with the first three health states are not likely to significantly impact the final result, since that figure is dominated by the DALYS derived from deaths (mainly from people aged 60+) and the associated Life Years Lost.

As noted earlier, the fatality data used in this calculation only included those that died as hospital patients. The inclusion of non-hospital patient deaths would result in a larger calculated figure. This may be a significant source of uncertainty in this calculation.

The numbers of Life Years Lost are important to the final calculation, and depend upon the applicable age-specific life expectancies. The data used here are from Australia and different figures may be appropriate for other populations.

Some may argue that the true rate of infection may be much greater than the confirmed rate of infection with SARS-CoV-2. However, since unidentified infected people are likely to have very mild (or nil) symptoms, the associated DALYs with these cases would also be very low.

It is also possible that there are other health outcomes, which are not yet well understood. Given the large number of people, globally, who have now been infected with this virus, it seems likely that any poorly reported symptoms must also be relatively rare. Such cases (by virtue of being rare), would also be unlikely to significantly add to the overall DALY burden.

Alternatively, we may learn that there are infact additional severe and long-term impacts of COVID-19 for a sizable portion of the population, which have not yet been identified, -perhaps because of delayed onset of the illness. If that proves to be the case, the figures derived in these calculations will require revision.

Let me know what you think…

Addendum (31 May 2020)

Given reports of the Australian fatality rate for COVID, particularly for people aged 70+, the DALYs-per-case figure calculated above may be significantly underestimated.

This preprint by Peter Collignon and John Beggs reports more precise fatality data for Australia:

Incorporating that fatality data gives a much larger figure for “Life Years Lost”:

Once this figure is incorporated into a final DALYS-per-case number with the other three health states, the two hospitalised health states (“hospitalised” and “ICU”) become effectively irrelevant since the final sum is so significantly dominated by this one factor (deaths). A very slight additional contribution comes from the “non-hospitalised” health state, but this is at the level of the third significant figure, -a level of precision not supported by most of the input data.

After more consideration, I have also concluded that the “Disability Weight” for patients in intensive care (ICU) should also be “1”, rather than 0.778 as shown above. This is because patients in intensive care can be considered to be completely incapacitated. Most would be reliant on ventilators to breath and some would not be conscious. Nonetheless, this value is not significant to the final sum for DALYs-per-case, so this change does not affect the calculated result.

Given these considerations, based on primarily Australian data, COVID-19 can be estimated to have a DALYs-per-case value of 0.126.

SARS-CoV-2 RNA concentrations in primary municipal sewage sludge as a leading indicator of COVID-19 outbreak dynamics

There are now rapidly increasing numbers of (non-peer reviewed) pre-prints and (peer-reviewed) published papers describing the application of wastewater-based epidemiology for COVID-19. This involves measuring the presence of SARS-CoV-2 RNA in municipal wastewater (sewage) and using those measurements to infer spatial and temporal patterns of infection in the community.

Some of the most high profile reports so-far have been from The Netherlands, Brisbane (Australia), Paris (France), Massachusetts (USA), Montana (USA), Milan and Rome (Italy) Milan (Italy), and Spain. Although there is great variability among the methods applied and the way the data are interpreted, the evidence base for the general viability of wastewater-based epidemiology for COVID-19 has grown with each of these reports.

A new pre-print paper from Yale University (USA) was recently added to the list and is making quite a splash on social media. This paper is titled “SARS-CoV-2 RNA concentrations in primary municipal sewage sludge as a leading indicator of COVID-19 outbreak dynamics”.

The most novel aspect of this paper is that the researchers chose to use primary sludge as the medium from which to extract and measure SARS-CoV-2 RNA. This is different to all of the other papers, which have focused their efforts on raw wastewater (untreated sewage, usually from the inlet works for a sewage treatment plant).

Primary sludge is a product of primary wastewater treatment, and consists of a water solution carrying a higher load of suspended solid material, which has been separated from the main wastewater stream by settling under gravity. The paper states that the samples were collected at the outlet of a gravity thickener, ranging in solids content of 2.6% to 5%.

A possible advantage of using primary sludge, is that the primary treatment and sludge collection processes may involve a degree of mixing, beyond that to which the raw wastewater may have been exposed. This is potentially helpful since it may lead to an “averaging” of an otherwise highly variable signal. If some of the (effectively random) variability can be removed from the samples, quantitation may become more meaningful and easier to interpret.

It may also be that the RNA is more concentrated in the sludge than in the raw wastewater. This would depend on partitioning of the RNA to the solids material that is settled under gravity. The method states that 2.5 mL of well mixed sludge were added directly to a commercial kit optimised for isolation of total RNA from soil.

It’s difficult to compare between the published studies, since there are many confounding factors to consider. However, the authors state that “Due to the elevated solids content and the high case load observed during the outbreak (~1,200 per 100,000 population), the concentrations of SARS-CoV-2 RNA reported here ranged from two to three orders of magnitude greater than raw wastewater SARS-CoV-2 values previously reported”.

Working with more complex matrices (such as sludge) also has disadvantages, one of which is often a higher detection limit than can be achieved with cleaner matrices. The authors state “SARS-CoV-2 viral RNA was detectable in all samples tested and ranged from 1.7 x 103 virus RNA copies mL-1 to 4.6 x 105 virus RNA copies mL-1. The lower concentration in this range corresponds to a qRT-PCR cycle threshold (CT) value of 38.75 and can be considered a detection threshold for this method and sludge matrix”.

But these methodological details are not the reason why this pre-print paper has attracted so much attention on social media. Instead, it is the claim presented in the paper that this approach to wastewater-based epidemiology can provide a highly accurate 7-day leading indicator of COVID-19 clinical testing data and a 3-day leading indicator of hospital admissions.

In particular, a highly smoothed curve (using LOWESS smoothing) comparing VIRUS RNA concentrations (per mL) with clinical reporting of new cases of COVID-19 appears very impressive and has been widely shared.

It seems apparent that this smoothing technique does require some reasonable amount of consecutive data to achieve. So whether it can be effectively achieved 7 days ahead of clinical testing data is unclear. From my understanding, standard LOWESS smoothing involves averaging several datapoints around each datapoint. This type of “prediction”, could this only be done retrospectively. Restrospective prediction would be of more limited value than real-time prediction. Furthermore, there is a question of how quickly this data could be acquired and processed, -which would further limit the predictive usefulness.

Note: The quoted R=0.994 in the paper and the above tweet are almost certainly not meaningful since this appears to have been acquired from from (at least one of ) the smoothed curves. Hopefully some of these statistical limitations (and over-statements) will be ironed out during peer review.

We’d be interested in your thoughts!


Peccia, J., Zulli, A., Brackney, D. E., Grubaugh, N. D., Kaplan, E. H., Casanovas-Massana, A., Ko, A. I., Malik, A. A., Wang, D., Wang, M., Weinberger, D. M. and Omer, S. B. (2020) SARS-CoV-2 RNA concentrations in primary municipal sewage sludge as a leading indicator of COVID-19 outbreak dynamics. medRxiv, 2020.05.19.20105999.

Infectious SARS-CoV-2 in Feces of Patient with Severe COVID-19

A number of research papers have now reported the detectable presence of SARS-CoV-2 RNA oligotides in the faeces of infected patients. Some of these have previously been summarised on this blog here.

But the presence of RNA should not be misinterpreted to imply the presence of viable infectious virus particles (as has been pointed out many times on this blog, including here). Nonetheless, the evidence for some presence of infectious virions in faeces does appear to be slowly growing.

One example is this “Research Letter” published in Emerging Infectious Diseases. In this study, the authors describe the inoculation of Vero E6 cells from a human faecal sample and an observed cytopathic effect. This was followed by recovery of SARS-CoV-2 RNA from the inoculated cell culture, and then visualisation of recognisable viral particles by electron microscopy.

The authors of this study reported that they were able to isolate SARS-CoV-2 virus for 2 out of 3 patients that had previously tested viral RNA–positive from faecal specimens. They state that this indicates “infectious virus in feces is a common manifestation of COVID-19”.

The authors surmised that “isolation of infectious SARS-CoV-2 in feces indicates the possibility of fecal–oral transmission or fecal–respiratory transmission through aerosolized feces”. They concluded that “our findings indicate the need for appropriate precautions to avoid potential transmission of SARS-CoV-2 from feces”.


Fei X, Jing S, Yonghao X, Fang L, Xiaofang H, Heying L, Jingxian Z, Jicheng H and Jincun Z (2020) Infectious SARS-CoV-2 in Feces of Patient with Severe COVID-19. Emerging Infectious Disease journal, 26(8).

What are the implications of COVID-19 for purified recycled water?

Australian Water Association (AWA) Webinar:

The impact of the virus that causes COVID-19, known as SARS-CoV-2, cannot be overstated. Almost every aspect of our lives has been affected in some way. When thinking about potable reuse, exposure and transmission of SARS-CoV-2 can be expected to be prominent among community concerns. These concerns will likely be heightened if the use of Wastewater-Based Epidemiology, -to track the presence of the virus in sewage become a high-profile practice, which it appears set to do. Understandably, community members will want reassurance that potable reuse projects will not present elevated risks of exposure to SARS-CoV-2. This presentation will discuss the evidence that is currently available, as well as identify key knowledge gaps that should be targeted for addressing.

This Webinar is presented by Professor Stuart Khan – UNSW.

Date:      26th May 2020
Time:      4pm – 5pm (Australian Eastern Standard Time)

There will be a 40 minute presentation followed by a 20 minute Q&A session.

More information and registration here.

COVID-19: The environmental implications of shedding SARS-CoV-2 in human faeces

At a time when the world is so focused on the respiratory pathways of a respiratory virus, this recent paper in Environment International argues that understanding the opportunities for SARS-CoV-2 to be spread by the faecal-oral route must not be neglected. They state that the public health implications of significant concentrations of SARS-CoV-2 arriving at sewage treatment plants, and the consequent discharge into the wider environment are only just beginning to be investigated.

As previously documented on this blog, coronaviruses can remain viable in sewage for up to 14 days depending on the conditions such as temperature. However, the presence of solvents and detergents in wastewater can compromise the viral envelope.

The authors of this paper argue that although there is not yet any robust evidence for coronaviruses being directly transmitted by the faecal-oral route, the increase of viral load in the environment could increase potential human exposure. In particular, the transport of coronaviruses in water increases the potential for the virus to become aerosolised, particularly during the pumping of wastewater through sewerage systems and at the sewage treatment plant, and during its discharge and subsequent transport through the catchment drainage network.

Other situations where there is increased risk of human exposure from wastewater include high rainfall events which exceed sewage infrastructure capacity, resulting in discharge from combined sewer overflows and sewer flooding. The risk of exposure via the faecal-oral route is also of particular concern in parts of the world where safely managed sanitation systems are limited, and particularly where there are high levels of open defecation or other forms of non-sewered sanitation.


Quilliam RS, Weidmann M, Moresco V, Purshouse H, O’Hara Z and Oliver DM (2020) COVID-19: The environmental implications of shedding SARS-CoV-2 in human faeces. Environment International, 140, 105790.

New Paper: First confirmed detection of SARS-CoV-2 in untreated wastewater in Australia: A proof of concept for the wastewater surveillance of COVID-19 in the community

There has been some recent attention surrounding the potential to use molecular (i.e., RNA) detections of SARS-CoV-2 (the causative agent of COVID-19) in wastewater to track community prevalence. This approach, often termed Wastewater Based Epidemiology (WBE), has some potential advantages to case-by-case tracking, including improved throughput at the community level and tracking asymptomatic cases. It is critical to note that these detections do not represent culturable virus in the wastewater that would be necessary to cause infection; separate research is being conducted to assess the presence, persistence, and disinfection of SARS-CoV-2 in wastewater.

A recent paper led by Warish Ahmed at CSIRO and Jochen Mueller at the University of Queensland, and also including members of our research team at the University of Notre Dame, has demonstrated this as a proof of concept – First confirmed detection of SARS-CoV-2 in untreated wastewater in Australia: A proof of concept for the wastewater surveillance of COVID-19 in the community. Other recents studies in this vein has been published as preprints (e.g., Medema et al., Wu et al., Wurtzer et al.).

Ahmed et al. detected SARS-CoV-2 in two separate wastewater samples using two separate concentration methods, and detections were confirmed by sequencing. The number of infected individuals in the catchment area was also estimated using available virus shedding data and estimated per capita flowrates, and these values were within the same order of magnitude as clinical observations.

The study by Ahmed et al. and others supports the feasibility of WBE for tracking COVID-19 at the community level; however, critical questions remain to make these detections quantitative and predictive. One obvious area for future improvements includes methods for SARS-CoV-2 RNA concentration from wastewater. Nearly all reported SARS-CoV-2 RNA concentrations in wastewater have been low – this makes detection difficult. Specific areas to optimize the experimental methodology include viral RNA concentration and extraction, sample collection methods, and which molecular assays are used. In addition to improved methods, characterizing the efficiency of these approaches is necessary to refine prevalence estimates. For example, if the RNA concentration methods are 10% efficient, this would increase community prevalence estimates ten fold. Beyond method improvements, the current greatest source of uncertainty is the fecal shedding rate of SARS-CoV-2. Available data suggests these values vary by greater than five orders of magnitude both temporally and between cases – this results in model uncertainty greater than all other factors!

There is clearly significant research interest in developing WBE for SARS-CoV-2 monitoring. I hope that these early positive developments encourage continued development and research support of this promising area, both for COVID-19 and future infectious disease outbreaks.

World Health Organization leadership on water, sanitation and hygiene reducing COVID-19 impacts

Most people working in the water, sanitation and hygiene (WASH) sector are familiar with the Water Safety Plan (WSP) approach that was developed and proactively promulgated globally by the World Health Organization (WHO).

The WSP approach involves identifying reasonably foreseeable contamination events and then reducing the risks posed to acceptable levels by implementing operationally reliable and technically credible barriers. Importantly, the WSP approach isn’t reactive in that it doesn’t await the occurrence of contaminating events or the detection of contamination. Rather, the approach anticipates their potential occurrence, and the maintenance of adequate barriers, in a preventive manner.

Building upon the successful WSP program, WHO more recently developed and promulgated the Sanitation Safety Plan (SSP) approach. This adopted the same preventive risk management principles as the WSP approach.

WHO played the leading role in undertaking proactive work for over 20 years in developing and promulgating first the WSP, and then the SSP, approaches which are now firmly embedded globally. This work has involved review of evidence, advocacy, guideline development, training and dissemination programs, setting up partnerships and a wide range of supporting activities. The guidance is subjected to ongoing review and revision.

The focus on preventive barriers, rather than reactive response to the detection of contamination, is relevant to the COVID-19 outbreak. Fortunately, transmission via drinking water and wastewater is not considered an important or significant transmission route for the COVID-19 virus. But importantly, even if it were, the WHO’s WSP and SSP approach requires first and foremost consideration of risks from pathogens. The more numerous, environmentally robust and disinfection-resistant ‘worst case’ pathogens set the standard that needs to be achieved for the assessment and mitigation of such risks. Evidence to date suggests that a technically sound and robustly implemented WSP or SSP, developed to meet current good practice standards, provides a framework that also protects against transmission of the COVID-19 virus via drinking water or sanitation pathways.

This case study provides a useful illustration of the benefits of the WSP and SSP approach. The requirement to implement preventive barriers to the ‘worst case’ of the better-understood pathogens provides an inherent ability to mitigate many emerging pathogens. Under this preventive risk management paradigm it wasn’t necessary to detect the COVID-19 virus before water-related transmission could be mitigated. The only note of caution is that future emerging pathogens, or changes in environmental or other circumstances, might create challenges not adequately addressed by current barriers.

Another area in which WHO’s leadership has been very much in evidence during recent months is their rapid review of the evidence and development of WASH sector guidance relating to COVID-19. Once again, whilst water and wastewater haven’t emerged as important or significant transmission routes for the disease, there were concerns among communities and workers that needed to be addressed. In addition, hygiene has emerged as a major component of controlling the spread of the COVID-19 virus. WHO’s statements have been extremely reassuring and helpful to the WASH sector and the communities that are looking for reliable advice. As is common practice for WHO, they drew from a wide body of global experts within the WASH community of practice (such as Dr David Cunliffe from Australia) in developing their response.

In considering the implications for COVID-19 for the WASH sector WHO began by firstly understanding the concerns and questions that needed addressing to help prioritise its review of evidence and development of guidance. Secondly, WHO put together guidance that drew from the best existing evidence and information. Finally, WHO disseminated that information rapidly through their global networks and in multiple languages. As is normal practice for WHO, that guidance is subject to rolling review and revision in response to feedback from its intended audiences – both to incorporate new evidence, and to respond to feedback on user needs. The guidance includes advice on drinking water, sanitation, safety of workers and various aspects of hygiene. Importantly, the guidance is evidence-based, is subjected to extensive scrutiny by a global body of experts, contributors and users, and is proactively disseminated throughout the world. Despite this technical rigour, the guidance was developed and issued rapidly.

The WHO WASH resources are made freely available to all and in many languages. They can be accessed on the internet (here) and a recent update of note is the WASH and COVID-19 resources page. The site can be kept handy for the latest updates and revisions to documents but you can receive automatic updates simply by emailing with the text “subscribe WATERSANITATION” in the body of your email.

There are a wide range of resources available to support WSPs and SSPs. In addition there are various simple guidelines and posters on matters such as hand hygiene and use of gloves. We’ll leave you to browse more at your leisure, as well as to think about how you can contribute your evidence and case studies; and to provide feedback to WHO on the sort of guidance and support that you think is needed.