The virus responsible for the COVID-19 pandemic, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), primarily spreads through respiratory droplets and aerosols expelled by an infected person. Since the virus is shed in the feces of infected individuals, concerns arose regarding potential waterborne transmission through drinking water, recreational areas, and wastewater systems. While the virus’s genetic material can be detected in various water matrices, research indicates that the risk of infection through contact with properly treated or natural water is extremely low. The stability and infectivity of SARS-CoV-2 are heavily dependent on the type of water and the environmental conditions it encounters outside of a human host.
Survival of SARS-CoV-2 in Untreated Water Sources
SARS-CoV-2 is an enveloped virus, meaning it is surrounded by a fragile outer layer made of lipids (fats), which makes it particularly susceptible to disinfectants and environmental stress. This lipid envelope is crucial for infection, and its degradation rapidly reduces the virus’s ability to infect cells. The virus’s infectious particles degrade relatively quickly in untreated aqueous environments like river or tap water, with a 90% reduction in viability often occurring within one to two days at room temperature.
The temperature of the water plays a significant role in how long the virus remains viable. Lower temperatures, such as those found in cold water or at 4 degrees Celsius, can allow the infectious virus to persist for significantly longer periods, sometimes for more than a week. Viral stability is also influenced by other factors, including the presence of organic matter and microbial activity, which are higher in untreated wastewater and can contribute to faster inactivation.
It is important to distinguish between the presence of infectious virus particles and the detection of viral RNA, which is the virus’s genetic blueprint. Researchers can detect SARS-CoV-2 RNA fragments in water for weeks after the infectious virus has been inactivated, as the RNA is more stable than the complete viral structure. Therefore, the mere detection of viral RNA in a river or lake does not equate to a public health risk from infectious virus transmission.
Assessing Risk from Municipal Drinking Water
The risk of contracting COVID-19 through municipal drinking water is considered negligible due to the established treatment processes used by public water systems. Standard water treatment involves multiple steps designed to remove or inactivate a wide range of pathogens, including viruses far more resilient than SARS-CoV-2. The process typically includes coagulation and filtration, which physically remove particles and microbes, followed by a disinfection step.
Disinfection is usually accomplished with chlorine, chloramines, or ultraviolet (UV) light, all of which are highly effective against enveloped viruses. Chlorine works by penetrating the fragile lipid envelope of SARS-CoV-2 and reacting with the internal viral proteins, which destroys the virus’s ability to function. Because the virus is so sensitive, the concentration of disinfectants routinely maintained in public water supplies is more than sufficient to inactivate any potential SARS-CoV-2 particles.
This multi-barrier approach provides a high degree of assurance that the water reaching the tap is safe. Given the effectiveness of the treatment process, the scientific consensus is that drinking tap water poses no risk of COVID-19 infection.
Safety Protocols for Recreational Water
Recreational water environments, such as swimming pools, hot tubs, and man-made water parks, are low-risk for SARS-CoV-2 transmission when properly maintained. The safety of these waters relies on the use of chemical disinfectants, primarily chlorine and bromine.
Studies have demonstrated that the concentration of free chlorine typically found in a well-maintained swimming pool can rapidly inactivate SARS-CoV-2. For instance, a free chlorine concentration of 1.5 parts per million (ppm) at a pH between 7.0 and 7.2 can reduce the virus’s infectivity by more than a thousand-fold in just 30 seconds. Pool operators are generally advised to maintain:
- A free chlorine level of at least 1.5 ppm.
- A pH level between 7.2 and 7.6 to ensure effective disinfection.
In large natural bodies of water, like oceans and lakes, the risk is further mitigated by the massive dilution factor. Even if viral particles were introduced, the sheer volume of water quickly disperses them to levels where the chance of encountering an infectious dose is negligible. For all recreational settings, the primary risk of COVID-19 transmission is not the water itself but rather the close person-to-person contact that can occur on pool decks, in locker rooms, or in crowded beach areas.
Wastewater Monitoring: A Public Health Tool
The detection of SARS-CoV-2 in wastewater has emerged as a valuable public health surveillance technique. This practice, known as wastewater-based epidemiology, involves sampling raw sewage to measure the concentration of viral RNA fragments shed in the stool of infected individuals.
The viral load in sewage can act as an early indicator of community infection trends, often showing an increase in cases before they are reflected in clinical testing data. This is possible because people begin shedding the virus in their feces even when they are asymptomatic or before they seek a clinical test.
This monitoring detects non-infectious RNA fragments and is used for tracking disease prevalence, not for assessing the direct risk of infection to the public from the sewage itself. Although wastewater contains viral RNA and, for a short period, potentially viable virus particles, standard wastewater treatment processes are effective at removing or inactivating the virus. Exposure to wastewater is not considered a significant route for COVID-19 infection.