Many people wonder why rainwater is usually fresh (contains little salt), while seawater is very salty and unfit for drinking. Rain and the sea are part of a single water cycle, but the reason for this difference in taste is quite simple.
Firstly, solar heat warms the water in seas, rivers, lakes, and ponds. When heated, some of this water turns into vapor and rises into the atmosphere. A simple example can be imagined: if you add salt to a glass of water and heat it, the water will evaporate, and the salt will remain in the glass. The same thing happens in the sea: the water evaporates, but most of the salt dissolved in it remains in the sea itself.
The water vapor that rises into the sky enters cooler air. Upon cooling, the vapor begins to condense again into tiny droplets. Many such small droplets combine to form clouds. When the droplets in the cloud become too numerous and heavy, they fall to the ground as rain. Thus, the sun heated the water, it turned into vapor, the vapor rose, clouds formed, and then the water returned to the ground as rain.
The main answer is that when seawater evaporated, the salt remained in the sea. This is why rainwater does not contain as much salt as seawater. Nevertheless, rainwater is not absolutely pure; during its fall from the sky, it can collect dust and other fine particles.
It is also necessary to understand where the large amount of salt in the sea comes from. When rain falls on the ground, it comes into contact with soil, rocks, and cliffs. These rocks and soil contain various minerals. Rainwater carries some of these minerals. Then this water flows into small streams and rivers, which carry the dissolved minerals to the sea. This process takes a very long time, and as a result, various minerals and salts accumulate in the sea, making the seawater salty.
The process can be explained very simply: seawater is heated by the sun, turns into vapor and rises up, leaving the salt in the sea. The vapor cools in the atmosphere and forms clouds, which then cause rain. The rain falls onto the ground, collects minerals from the soil and rocks, and these minerals reach the sea through rivers. After that, the sun heats the seawater again, and the entire cycle starts anew.
Although rainwater contains little salt, this does not mean it can be drunk everywhere without treatment. Dust and other particles that have entered from the air may be present in raindrops. Furthermore, if rainwater is collected from a roof or a dirty area, it may contain dirt and microbes. Therefore, rainwater must be properly purified and filtered for drinking.
Simply put, the sun heats seawater, it evaporates, but the salt remains in the sea. This vapor forms clouds, which then cause rain. Therefore, rainwater is not as salty as seawater. At the same time, minerals and salts constantly enter the sea through rivers that take them from the land, maintaining the salinity of the seawater.
