The COVID in WC

There are several posters published by the Generalitat de Catalunya that contain recommendations to prevent the spread of Covid in public spaces. Apart from the usual ones such as the use of a mask, washing hands, using hydroalcoholic gels or ventilating the spaces well, there is an enigmatic recommendation. A toilet with two numbers appears. Number 1 marks the toilet lid and number 2 marks the toilet discharge. How is it interpreted? When we have used the toilet, we must lower the lid before flushing. The reason is that the massive fall of the water discharge to drag the filth into the sewer can generate aerosols that contain microparticles of feces and eventually pathogens, as pointed out by a study of fluid dynamics carried out by several teams of Chinese scientists. An example to visualize it is observing a waterfall of a river. When the water falls from a certain height and hits the water in the pool at the base, a large amount of aerosols are created that, pushed by the wind, wet the entire environment (and its visitors), creating conditions of high humidity, in which an exuberant vegetation usually proliferates. In the bathroom, aerosols from the toilet flush can be deposited on all surfaces several meters away, and contaminate items such as the toothbrush or even be inhaled by the next user of the bathroom.
Some studies indicate that the Covid virus can be present in the feces of infected people even if they are asymptomatic. It is not known if the inhalation of viruses of fecal origin is a route of contagion, but for precaution and hygiene, it is highly recommended to lower the toilet lid before flushing.
On the other hand, it is also necessary to ensure that all the drains in the house have accumulated water inside the siphons, and thus avoid entering bad odors from the sewer and eventually aerosol particles.