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Sarah Wolfe is an associate professor in the Faculty of Environment at the University of Waterloo. She is currently a visiting professor at Royal Roads University.

We know little about how the novel coronavirus might survive and move within our drinking and wastewater systems. But in some regions such mechanisms could be a critical piece of the puzzle surrounding the disease transmission.

To understand why, we need to look more generally at how modern societies manage their water supplies and waste. We’ve learned the hard way to value clean water. Hepatitis, dysentery and cholera arrived via contaminated water in relentless deadly waves prior to the 20th century.

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Since then, good science and engineering have helped us build integrated systems that link drinking, waste and storm water management. In ideal circumstances, these systems remove disease-causing contaminants from drinking water sources. Our urban wastewater treatment systems then clean our waste tap and toilet water (water that’s often combined with storm water runoff from rain or melting snow) to make it safe enough to release back in to surrounding streams, rivers, lakes and oceans. Drinking water and wastewater treatment is one of our great public-health success stories.

Despite this success, water supply systems around the world face two persistent and interconnected problems that have major health implications. Growing urban populations are combining with climate change to put ever greater demands on wastewater services; and we’re fighting a continuing battle to stay ahead of the constantly evolving pathogens that can make us sick.

Wastewater treatment plants may be built too small for growing populations or not maintained because of high costs. Also, climate change is causing more intense, frequent rainstorms. Particularly in concrete-covered cities, storm water can easily infiltrate and overload a sanitary system, causing the release of untreated wastewater into surrounding waters.

For example, the low-lying city of Wuhan, China – where the COVID-19 pandemic originated – paved over almost 100 naturally occurring lakes in a rush toward massive urbanization. Wuhan also has an abysmal wastewater treatment system.

According to the Asian Development Bank’s environmental assessment report, the city is served by a mixture of antiquated wastewater, storm water and combined sewer networks. In 2000, Wuhan produced more than two million cubic metres of wastewater a day, of which just 6 per cent was treated; 94 per cent was released without any treatment into surrounding waters. The ABD invested millions in Wuhan’s facilities to increase the amount of wastewater treated and prevent summer monsoon storm water from overloading the system and repeatedly washing millions of cubic metres of sewage into the city’s drinking water supply. Combined sewer overloads during the rainy season continue to negatively affect the local waters.

The second big challenge is that the bugs that make us ill are constantly evolving. These pathogens include not only relatively large bacterial cells but also viruses, tiny pieces of genetic code that take over human cells to replicate themselves. Some of these pathogens pass through us and end up in our toilets.

The COVID-19 illness manifests itself through both respiratory symptoms (coughing and difficulty breathing) and gastrointestinal symptoms (vomiting and diarrhea). Experts consider coughing and droplet transmission to others to be the most prevalent transmission mechanism. But in recent studies from China, patients presented with diarrhea days before the fever and respiratory symptoms appeared. Other research showed that the virus sheds into stool and that 23 per cent of patients “remained positive in stool after showing negative in respiratory samples.” In other words, transmission of the virus through feces may be possible even after the virus clears from the respiratory tract.

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In addition to the new coronavirus and the one that caused the 2003 SARS outbreak, a number of other coronaviruses circulate in the human population, including some that cause the common cold.

In a 2015 article in the journal Environmental Science: Water Research & Technology, Krista Wigginton at the University of Michigan and her colleagues proposed that fecal-oral transmission of a coronavirus could occur through the urban water cycle. They cite research that found coronavirus genes in more than 80 per cent of untreated wastewater tested.

Although they note there is no effective tool to measure the load, viability (infectivity) and persistence of a given coronavirus in stool and wastewater samples, they suggest two possible fecal-oral transmission routes. First, intense storm water events may trigger sewer or septic overflows that releases viruses into surface or ground waters that are in turn used as drinking water. Second, viruses moving through a treatment facility may generate droplets and surface contamination that infect workers who then go on to transmit the disease within their communities.

David Johnson of the University of Oklahoma and his colleagues have shown that leaking sewage pipes and toilet flushing can generate virus-laden aerosols that survive on surfaces and potentially contribute to disease transmission in public facilities. For example, flushometer toilets – the automatic flushing models now ubiquitous in health care and public bathrooms – produce the greatest number of droplets per flush.

Five years ago, referring to the 2003 SARS coronavirus, Dr. Wigginton and her colleaques concluded that “it is quite plausible that a highly virulent new coronavirus like SARS-CoV will emerge in the future and pose challenges for water and waste water industries.” (The new coronavirus that causes COVID-19 is a type of SARS virus; it has been given the label SARS-CoV-2.)

Given what little is known about how the new coronavirus might be transmitted in integrated water and wastewater systems or surfaces, additional research is desperately needed. In the meantime, lower the toilet lid when you flush, wash your hands with soap, don’t touch your face, and thank your municipal water and wastewater professionals for everything they do to keep us safe and healthy.

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