CHINA  The next time you go to the bathroom, you might want to consider closing the toilet lid before flushing. Researchers from China say that when toilet water swishes around the bowl, its flow becomes quite turbulent and creates vortices that carry droplets of toilet water into the air.

If you’ve got magazines, decorations, and extra toilet paper rolls close by, you may want to move them further away. Researchers warn these droplets can travel to a height of three feet and may land on nearby surfaces. They could even get inhaled accidentally.

Many viruses and bacteria can live in the digestive tract and end up in waste, including the SARS-CoV-2 virus. Toilets might be one of the methods of transmission this new virus has been using to spread around, researchers warn.

## Toilet testing

For the study, the authors used basic fluid dynamic equations to create computer simulations of the flow of water and air in two types of toilets: one with a water inlet for flushing, and another with two water inlets.

The model shows that as the water leaves the inlet and strikes the opposite side of the bowl, it creates turbulent vortices of water and air that mix together. This process causes the formation of tiny water particles that can spread around pretty easily.

Researchers created computational models to track the spread of these microscopic particles. The model shows that the droplets fly about three feet above the bowl, and they can stay in the air for about a minute since they are so small.

The only difference the researchers found between the behavior in each model is the speed at which the droplets travel. The size of the “cloud” of droplets the two toilets create is pretty similar.

## Frequent use may create stronger clouds

The researchers add that the droplets travel at a greater speed the more a toilet is used. “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,” says co-author Ji-Xiang Wang, of Yangzhou University, in a press release.

The simple solution to this problem is to close the toilet lid before flushing. However, this isn’t quite possible in the public restrooms in countries where commodes don’t have lids. Researchers recommend that all toilets have lids, and they even suggest a redesign of models that automatically shut the lid before flushing.

The study is published in Physics of Fluids.

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