Why are there different types of water in nature?

Have you ever wondered why the water in the ocean is salty while the water in rivers and most lakes are fresh?

Believe it or not, seawater originally was fresh, but that changed millions of years ago. Now, a gallon of seawater has about 4.5 ounces of salt, on average. Or, roughly 35 grams per kilo of water.

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Things changed dramatically 4 billion years ago when Earth's temperature started to cool off.

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The first seas emerged thanks to the rains that poured on our planet for thousands of years: the water ended up in lower areas, creating the seas.

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Flowing rainwater carried mineral salts that ended up feeding these seas and oceans.

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87% of sea salt is made up of sodium chloride, which is what your common, everyday kitchen salt in a saltshaker is made of. The rest is magnesium sulfate, an element that gives the water a bitter taste.

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Even after seawater evaporates, salt remains there, keeping the same saline level despite the renewing water.

That's how, over thousands of years, the continuous flow and evaporation of water from the seas and oceans has left a bigger and bigger deposit of mineral water reaching the levels of salinity we have today.

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Other elements that affect the saline levels of water are depth and weather. The deeper the water level, the higher the salinity while in places where it rains more, the salinity is lower.

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The presence of rivers also affects the levels of salinity. Bodies of seawater connected to rivers tend to be less salty due to the constant supply of fresh water.

At this point, you might ask yourself where does fresh water come from?

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Rivers are fed by rain, which in turn is possible thanks to the water evaporation in oceans and other large bodies of water. When seawater evaporates, the salt is left behind, turning it into fresh water when it returns to its liquid state.

In fact, water from rivers carries a small percentage of sodium chloride, too low to be detected when we drink it.

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Besides rivers, lakes are generally made up of fresh water. Freshwater lakes were probably formed thanks to glaciers melting over time.

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It's important to mention that there are also saltwater lakes. These are usually formed in landlocked basins. Like the seas, they acquire their salinity through deposits of accumulated mineral salt.

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The largest example of a saltwater lake is the Caspian Sea, between Europe and Asia and with a surface of 143,200 mi2 (371,000 km2). Other important examples around the globe are the Dead Sea and Utah's Great Salt Lake.

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