Flushing your toilet may be releasing clouds of aerosol droplets containing bacterium and viruses – including coronavirus – that may linger in the bathroom air and on its surfaces, waiting for another person to inhale or otherwise come into contact with it.
Turbulence caused by flushing a toilet can spread both bacteria and viruses like SARS-CoV-2, the coronavirus responsible for COVID-19. Previous research suggests that the virus may be transmitted through poop in addition to coughing and the Centers for Disease Control and Prevention (CDC) notes that coronaviruses on surfaces and objects “naturally die within hours to days,” warning that toilets are among a list of surfaces and objects that are frequently touched and require routine disinfection.
To determine how flushing a toilet might facilitate the spread of viruses and bacteria, researchers at Yangzhou University in China created computer models to simulate how a flush affects the water and air flows and, subsequently, a “cloud” of aerosol droplets. This was done by using the Navier-Stokes Equations, a standard fluid equation that NASA writes “describe how the velocity, pressure, temperature, and density of a moving fluid are related.” Developed in France in the 19th-century, the Navier-Stokes Equations are complex and account for how fluids may flow given certain parameters, such as simulating the flushing of two types of toilets – one with a single inlet for flushing water and another that creates a rotating flow. The team then incorporated a model to simulate what droplets would be ejected from the toilet bowl and into the air by building on previous research that estimates how aerosol droplets are ejected when a person coughs.
Nearly 60 percent of particles ejected from the bowl was shown to rise high above a toilet seat from those with two inlet ports largely due to the great level of velocity, which creates more aerosol movements. On one-sided toilets, it was shown that as water pours into the bowl from one side, it hits the opposite side and creates vortices that move up and out of the bowl nearly a meter (3 feet high), which can be inhaled and settle onto surfaces.
"One can foresee that the velocity will be even higher when a toilet is used frequently, such as in the case of a family toilet during a busy time or a public toilet serving a densely populated area," said co-author Ji-Xiang Wang, of Yangzhou University in a statement.
The solution is simple. The researchers note that just putting the lid down when flushing could help to alleviate the spread of viruses and bacteria-containing aerosols, conclude the authors in the journal Physics of Fluids.