No one really knows the amount of fresh water on earth in litres but it has been said that 2.5% - 2.75% out of all waters on earth is fresh water.
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Because this claim has been around for years, I think one day, if we do not pay attention, we may lose over 50% (+1% of fresh water diverted to saline water) of our fresh water.
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Not only do we pollute our streams, but we consume too much water and we run our streams dry. Yes, one of the main reasons why our rivers runs dry is because we drain too much water water from those rivers. Thousands of litres.
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In my simple maths, if 1 person consumes a minimum of 30l/day, then 7.64 billion people consumes over 229 000 000 000l/day ( over 229 billion litres in 1 day). It is even more because farms use Thousands and thousands of water for irrigation than we do for the domestic use.
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This simply means that, if the world hits 10billion people in near future, there will be high chances of "Fresh Water scarcity problems" than we have today.
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Remember, once we use the water, it is no longer clean. The more the population, the more the water problems we will face.