There is no credible evidence to prove that the rainwater is effective at destroying the COVID-19.
The COVID-19 spreads mainly through close contact from person-to-person, and some people without symptoms could spread the virus. A person can likely get COVID-19 by touching a surface or object with the virus on it and then touching their mouth, nose, or possibly their eyes.
Jared Baeten, the professor of global health, medicine, and epidemiology at the University of Washington, said that rain reduces the infection and can physically wash it off a surface just like dirt. But experts do not believe rain deactivates the virus or disinfects surfaces the way soap and water does. While this is the case for influenza, some studies show that more research is necessary to prove such claims. As of now, claims related to weather conditions and the transmission rates of COVID-19 relation remain non-conclusive. The only effective methods to disinfect and clean the surfaces recommended by the Centers for Disease Control and Prevention(CDC) are alcohol(70 percent) and the United States Environmental Protection Agency(EPA)-registered household disinfectants.
The COVID-19 pandemic has given rise to a lot of potentially dangerous misinformation. For reliable advice on COVID-19 including symptoms, prevention and available treatment, please refer to the World Health Organisation or your national healthcare authority.