Answer:
The easiest answer to that is that most of the water on Earth isn’t just water.
Explanation: Most of the water on Earth contains high levels of salt, and that’s a major cause for why so much of that water is not fit for human consumption. That much salt is toxic to humans because it overloads the kidneys’ ability to remove salt. Freshwater works in part by diluting and absorbing the salt in your body so it can be flushed out of your system, but salt water is so saturated in salt this just isn’t possible. Even worse, the salt in the salt water actually adds to the salt in your body, so when you are dehydrated, one of the worst thing you can do is drink salt water.
About 97% of the water on Earth is salt water. Of the remaining 3%, some of that will be unfit for human consumption because it was used in industrial processes or sanitation, and some of it will be unfit for human consumption because the water is home to parasites (and in some cases, the water is both).
As a sidenote, when I said that the remaining 3% of the water was not salt water, I didn’t say that it was available freshwater (tainted or otherwise). Most of the freshwater in the world is ground water, literally water that is found in the ground itself.
Hope that helped you <3 ;)
