The Spanish National Research Council, which falls under the ministry for science and innovation, has submitted the report about the relationship between coronavirus and water/beaches that had been requested by the secretary of state for tourism.
The council's report is based on available scientific information, so it makes clear that there aren't specific data for SARS-CoV-2, which is the coronavirus strain that causes Covid-19. This caveat aside, the report states that where seawater is concerned, the "dilution effect" and the presence of salt will probably contribute to a decrease in viral load. This is what happens with other viruses for which there is information.
In pools and also in spas, the use of disinfecting agents that is standard practice prevents microbial contamination by users - microbial referring to microbes that cause disease. This disinfection should therefore be sufficient to make coronavirus inactive. In addition, aerosols used for spas have a similar disinfecting effect, while the high temperatures for saunas and steam rooms will reduce the probability of the virus surviving.
Although there is little likelihood of the virus being transmitted in seawater, the report does note the possible risk in situations where wastewater enters the sea, while it also draws attention to the risk from there being crowds of people in the sea - the same applies to pools. The principal risk is, therefore, from contact with anyone who has coronavirus and from "respiratory secretions" (coughing or sneezing). Because of this, the report says that recommendations for social distancing should apply as they would out of water.
Greater risk is posed by freshwater, where the possibility of virus survival is increased because of the absence of salt.
Where sand is concerned, the report states that conditions are favourable. There is very little probability of infection because of the combination of seawater salt, ultraviolet radiation from the sun and the high temperature of sand. Beach disinfection, the report adds, needs to be respectful of the environment.