About salt and sea water
Why is sea water salty?
If you have ever wondered why ocean water is salty while rainwater is not? It is because water, after pouring down from the sky as rain, forms streams and rivers that carry tiny salty particles they pick up from the rocks and soil they touch, taking them to the sea.
This is why the closer a river gets to the ocean the saltier it gets.
Why can't we drink seawater?
We cannot drink seawater for the same reason: because it is salty. Our bodies are prepared to take the water we drink and carry them to our cells; but our bodies usually need water to get rid of the salt we take in excess. Thus, if we drink seawater, we would force our bodies to use the water we drank and more to get rid of the salt excess we took with it. This, in the not-so-long term would unfortunately kill us of dehydration.
Why doesn't seawater kill fish then?
Nobody is absolutely sure about this, but the point is that seawater does not keep getting saltier and saltier all the time. Something in the oceans keeps salinity levels even, allowing life in them. Scientists suspect a chemical reaction caused by sun light or some bacteria, but it hasn't been proven yet.