Categories: Earth

Earth Has Less Water Than You Think


If you were to take all of the water on Earth — all of the fresh water, sea water, ground water, water vapor and water inside our bodies — take all of it and somehow collect it into a single, giant sphere of liquid, how big do you think it would be?

According to the U. S. Geological Survey, it would make a ball 860 miles (1,385 km) in diameter, about as wide edge-to-edge as the distance between Salt Lake City to Topeka, Kansas. That’s it. Take all the water on Earth and you’d have a blue sphere less than a third the size of the Moon.

Feeling a little thirsty?

And this takes into consideration all the Earth’s water… even the stuff humans can’t drink or directly access, like salt water, water vapor in the atmosphere and the water locked up in the ice caps. In fact, if you were to take into consideration only the fresh water on Earth (which is 2.5% of the total) you’d get a much smaller sphere… less than 100 miles (160 km) across.

Even though we think of reservoirs, lakes and rivers when we picture Earth’s fresh water supply, in reality most of it is beneath the surface — up to 2 million cubic miles (8.4 million cubic km) of Earth’s available fresh water is underground. But the vast majority of it — over 7 million cubic miles (29.2 cubic km) is in the ice sheets that cover Antarctica and Greenland.

Of course, the illustration above (made by Jack Cook at the Woods Hole Oceanographic Institution) belies the real size and mass of such a sphere of pure liquid water. The total amount of water contained within would still be quite impressive — over 332.5 million cubic miles (1,386 cubic km)! (A single cubic mile of water equals 1.1 trillion gallons.) Still, people tend to be surprised at the size of such a hypothetical sphere compared with our planet as a whole, especially when they’ve become used to the description of Earth as a “watery world”.

Makes one a little less apt to take it for granted.

Read more on the USGS site here, and check out some facts on reducing your water usage here.

Water, water, every where,
And all the boards did shrink;
Water, water, every where,
Nor any drop to drink.
– from The Rime of the Ancient Mariner, Samuel Taylor Coleridge
Jason Major

A graphic designer in Rhode Island, Jason writes about space exploration on his blog Lights In The Dark, Discovery News, and, of course, here on Universe Today. Ad astra!

View Comments

  • That is still a f^ckton of water any way you cut it. Imagine standing in Topeka and looking up from the ground at that thing.

  • That's a pretty tall ball of water - much taller than Hubble orbits and about 1/10 the diameter of the earth. Also consider that the Eart'h's crust, where most of the water lives, is very thin, no more than 70km deep.

      • Actually, it appears this only takes into account water in-and-above the crust; water present in the mantle wasn't accounted for (and I'm not sure we even have a reliable estimate of the water content of the mantle).

        • Considering that the Earth's mantle consists of liquid magma and pressurised solid rock, I think we can conclude that this estimate includes all the water.

  • For non-Americans, here are some more analogies to show how far 1,385 km is (the diameter of the ball). For Australians: Distance from Melbourne to Brisbane. For Europeans: Distance from Paris to Warsaw. For astronomers: The size of Sedna.

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  • Nothing like a reality check.

    Wonder how large a sphere needs to be to hold the denser part of the atmosphere...say up to 10,000 feet?

    • JM,
      I thought almost the exact same question this morning. So computing the size of a ball of atmosphere (all of it, at sea level pressure and density) comes out to 2087.86 km diam (1296.56 mi). That's only nominally larger than the size of the ball of water...

  • In one way it is not surprising, water only covers 2/3rds of the Earth's surface to a fairly shallow depth. (when compared to the diameter of our planet. ) It is a great reality check though.
    Roseland Observatory. UK.

  • And all that life-sustaining water is said to have been naturally out-gassed, and/or deposited by hail-storm of cometary impacts.

    However old the Earth actually is, that amazing aquamarine sphere has apparently been preserved through all Earth's living history, in the finest balance with the vast continental landmasses, and through all erosive processes and material transfers of time, from lands to seas, in dynamic change of ages.

    Though ocean levels have apparently been raised and lowered (or continental shelf regions themselves), from warm/cold climatic episodes (Ice Sheets/melt-offs), the breaking waves of endless shores, define the edges of its bulk to narrow tidal zones, ebbing and flowing only so far. Little changed over a span of life. In scales of landmass depths and ocean volumes, that is remarkable. As Earth's desolate Moon of fortuitous placement, works its silvery “magic” over our air-vaulted “Blue Planet”.

    Yes, indeed, “Water, water, every where”, a wonder of our world so fair.

  • What a huge amount of water!
    Only freshwater is about 300giga litre procapite considering 7 billions people living on the earth.
    Each human being could swim in a giant freshwater's droplet 80m in diam. (260 feet) , can you imagine it?
    Considering all of the water, the droplet's diameter should rise to about 270m (900 feet).
    It is enough freshwater to fill a personal square swimming pool 100m wide (330feet) and 30m (100 feet) deep.
    I feel... wet, not thirsty at all... ;-)

  • And that amount is becoming smaller and smaller isn't it? Rockets using liquid oxygen and hydrogen dump tons of water into space or does the exhaust fall back to earth? Correct me if I'm wrong.

    When I think about the fact that we are launching one rocket after the other the only thing I can think about is that we are discarding tons of precious metals and liquids/gases that we will never be able to recycle. It hurts.

    • Dude, stop being such a pansy! You're at the extreme end of the greeny spectrum, take a look outside every now and then it's not all doom and gloom. In the grand scheme of things, what's some fuel and metal in the name of science when you consider all the asteroids / meteoroids that come through the atmosphere everyday?! Seriously, it's depressing that you're so concerned about this.

      • If it helps, consider all the rockets to be an investment in future space-mining. There's water on the moon dontcha know!

    • they are developing a machine satalite that will go up and bring down obsolete sats from orbit..a space Junk vaccuum if you will...spend a drop get a drop back...sort of an endless cycle.

    • Who`s to say we won`t get hit by an asteroid next week, which replenishes all the water, but you can`t enjoy it for another 50 million years! (:

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