Why the water of the rivers is sweet

Fresh water refers to the water that is found naturally on the earth’s surface. Only 3% of the water on the planet is fresh and is found in different forms, such as:

• Layers of ice.
• Glaciers
• Icebergs.
• Lakes.
• Lagoons
• Wetlands
• Rivers.
• Streams.
• Underground, in aquifers.

This term “sweet” began to be used to mark a clear opposition to the term “salt water” of seas and oceans. The truth is that fresh water is not sweet as such, but is colorless and tasteless, and is characterized by having a very low concentration of dissolved salts in it, although we do not notice it on our palate. This means that fresh water also contains mineral salts such as calcium, silica, magnesium or iron, but not at the level of salt water.

The first step in trying to explain why the water in rivers, lakes, wetlands, etc., is sweet, is to understand the source of the water in these rivers and the whole process that follows, that is, to analyze the cycle of the water .

It is true that the source of practically all fresh water is precipitation, which can manifest itself in the form of rain, snow, or fog. In addition, the accumulated water in the form of ice and snow also produces a contribution of fresh water with the thaw.

With rainfall, fresh water reaches the earth’s surface. These precipitations already contain materials that were dissolved in the atmosphere from which they came, as well as from the sea or the land on which the clouds have moved until the moment of the “discharge” of water.

This water that reaches the earth’s surface seeps into the subsoil or slides down the ground if it is sloping, as can occur on mountain slopes. In this way it originates or feeds rivers that finally flow into the sea. Here, the water evaporates again and the cycle begins again with the formation of new clouds.

If at this point you still have not come up with an idea, we will provide you with a key piece of information. Numerous mineral substances and salts are found on the earth’s surface. This may give you some clue. With the water that falls through the precipitations the erosion of the terrestrial surface takes place, reason why these substances are dragged until the rivers and along the route of these until their mouths in seas.

From here we can conclude a first point, and that is that the salinity of seas and oceans comes from the substances dragged and transported during the water cycle. Although it is not the only reason.

But this first conclusion can also open another new doubt. Many rivers, before reaching the sea, flow into lakes and lagoons that do not have the salinity of these marine environments. So what’s going on? What piece of the puzzle are we missing?

Well, as we previously concluded, one of the reasons why the sea and oceans are salty is due to the different mineral salts and substances that are dissolved in it from rivers and the water cycle, in particular natural chemical elements. such as chlorine, calcium, partner, sulfur, potassium or magnesium. But as we also said, it is not the only reason.

The proportion of water in the seas and oceans is much greater than that in rivers and lakes, since most of the water on the planet is found in them. How can it be, then, that the contribution of small rivers causes such a large body of water to be salty? Well, the seas and oceans , unlike rivers, do not have water outlets , that is, the molecules that reach them remain for thousands of years in the oceans and seas when their water is not renewed. To this is added that the greatest phenomenon that occurs in these bodies of water is evaporation due to solar rays, which, by eliminating the water, but leaving these substances increases its concentration . This is the other reason why sea ​​water is salty, because the substances that reach it are “retained”.

With all the above information we should already be able to give an answer to this question.

Again, we remember that, although it is called “fresh water”, the water of rivers and lakes also contains mineral salts, although in low concentrations. We also said that when these rivers flowed into the seas and accumulated these substances in them, they made them become saline as they did not have outflow streams. On the contrary, in rivers, being in continuous movement, these substances remain for a short time . Here is the key.

And in the case of the lakes? The same thing happens with them. Although the rivers flow into them, the mineral salts do not accumulate , as the lakes have drainage systems and water outlets. Thus, the substances it carries disappear with the water that brought them, maintaining a low concentration of salts in these lakes and lagoons.

Finally, we can conclude that the water in rivers and lakes is sweet because the mineral salts and substances dissolved in the water do not remain stagnant and retained in it , but are quickly washed away into the seas and oceans.

Here below you can see a short video of a biologist professor who explains why the water of the rivers is sweet and that of the sea is salty.