Eli5 How is water renewable?

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Every bit of information I find just talks about water cycling through its different states of matter, I’m aware that water evaporates then rains and returns to the earth but none of them say at which point more water is actually produced or how. Is it actually renewable or is it the concept that there are other sources such as ice and humidity that can keep refilling our supply?

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Anonymous 0 Comments

The water on Earth is a fixed amount with very little loss or production of new water. No matter what you do with water, it just reenters the water cycle. It does not escape.

This is because the only way for it to escape is to leave Earth’s atmosphere and escape into space. Short of us building rockets to throw it out of Earth’s gravity well, the only mechanism for this is to float to the very highest reaches of the atmosphere and then get hit by the solar wind hard enough to be driven away from the Earth over time.

This happens with hydrogen and helium. However, a water molecule is too heavy to float that high and is too heavy for the solar wind to matter that much.

So, all water stays on Earth. On Earth, almost any way you can imagine to “use it up” simply puts it back into the water cycle.

Essentially, water on Earth is a nearly perfect recycling system. No new water need apply.

Edit: Corrected error on the rate of escape of hydrogen and helium.

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