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

46 Replies to “Earth Has Less Water Than You Think”

  1. 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.

  2. 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.

      1. 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).

      2. 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.

  3. 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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  4. 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?

    1. 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…

  5. 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.

  6. 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.

  7. 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… 😉

    1. Whether we feel thirsty or wet, better to conserve our water resources NOW!!

      1. Water resources are going no where, all you need to do it is purify it again.

  8. 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.

    1. 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.

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

    2. 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.

    3. 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! (:

  9. It is that big a volume only because water does not compress. Imagine all of earth’s atmosphere…stuff all of it into a large tank

    1. Atmosphere is very thin and is included in this measurement…as is ice and all other forms of water…its foolish to worry as its going to be the one thing that will limt the humans on this rock…after we kill off the other animals for their water

  10. “Makes one a little less apt to take it for granted.” – We’re talking humans here right? One of the reasons I want space exploration and colonization to go full speed ahead is *because* of my fellow humans. Very interesting article though 🙂

  11. I wonder if that incorporates atmospheric water, soil water, ice, and moisture in rock. It would be cool to see a pie chart of salt, fresh, and the others.

  12. Ok I’m going to be a bit snarky here. Soooo I guess the answer is to flush twice with the low flush toilets… Perhaps the better answer is to harvest glaciers and icebergs.

    This really comes down to population control doesn’t it? So… we then gotta figure out who gets the short stick… because I reckon the Libs won’t just volunteer to self-sacrifice… I mean just look at the big AGW champions… Those ‘conservatives’ of the Earth.

    Water is precious. I conserve what I can and have actively tried to use greywater on plants… But I’m a realist also. The 3rd world is not going to limit their promise at development and better lives just because we say so.

    Water will become more expensive and will become a resource that wars are fought over. I predicted this in the 70’s in a story about Virginia-NC fighting over Kerr Lake and other water resources. They’ve long had battles about shared water… California and the West have long fought over the Colorado.

    It’ll only get more exciting with time.

    Maurizo52 has a great point, it’s a bunch of water per person… but that is all the person gets for their entire life…and then they have to pass it down to the next generation…which will necessitate splitting it in atleast half. 5 billion in the 70’s I think and now 7 billion 30 years later??? 10 billion perhaps in 15 years? My ‘droplet’ is shrinking, no matter WHAT I do….
    D@mn…. I am a RWC and sound like a Greenie. But math doesn’t lie.

    ohhh wait, it doesn’t matter. It still goes back into the tank called Earth to be reused like always!

  13. The Earth has a modest amount of water. A few of these extra-solar planets that have been found have water up to hundreds of kilometers in depth.


  14. What’s with the fresh water “100 miles across”? Seems like 50 miles radius would be 50^3 * 4/3 * Pi = about 1/2 million cubic miles… article then goes on to to say it’s 9+ million cubic miles. Perhaps it’s 200 miles across?

  15. Hey Jason, I think you’re missing a few zeroes in a couple of places.

    Paragraph 5:
    “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.”

    And paragraph 6, sentence 2:
    “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.) ”

    Shouldn’t they be 29.2 million and 1,386 million respectively?

  16. All the water on Earth could fit on the head of a pin if it was in a black hole.

    1. Actually it started out as “Dirt”, but a while after it got populated the popular vote went to “Earth”. (Well, it sounds better than “Soil”.)

      1. Are you saying that before we called our planet Earth, or Terra, we started out calling it “Dirt”? …Could you elaborate, how do you know this.

  17. If we had as much water as the asteroids have by content, we would drown in it.

    This is the only real finetuned constraint for technological life here.

    For the lower limit, it just so happens that Earth seems to be marginally large for having plate tectonics. (Compare with Venus and Mars.) It is water that is needed to make the subducting plates pliable enough.

    Water is also needed for massive granite formation, which is what makes up our less dense continental plate floats. It is believed that super-Earths can manage plate tectonics without the constraint of water.

    Luckily we had a large last impactor that blew off the excess volatiles into space. The Late Heavy Bombardment gave us both our ore metals (that had gone to the core during differentiation) and our volatiles back in sufficient quantity.

    That process is probably not to uncommon in planetary system formation. But it makes you wonder if the super-Earths are mostly water worlds.

    The amount of water on Earth is estimated as “one ocean below for one ocean above”. I.e. the crustal water is ~ as much as what we see above it. The mantle is too hot for crystal water I believe, so you get oxides and hydrides at best.

    This gives us that free water is ~ 5/1000 of Earth’s mass, IIRC.

    1. My guess is zero…if you mean contaminated by foreign substances, melted from ice caps or distilled from salt water then you should restate your question.

      1. Actually, water is created when combusting fossil fuels and, technically, you can “destroy” water by separating the hydrogen from the oxygen.

      2. Water molecules are also split during photosynthesis.

        I remember hearing as a kid a common misconception years ago, that we are drinking the same water that had once been urine in dinosaurs (Wowwww…! Ewwwww!)
        Soon after in high school biology I remember reading that all the water on the planet splits and bonds several times during a period of ten Ma., so our water is “new”.

    2. It is a water cycle, so what organisms or photolysis breaks down is reconstituted.

      For an estimate, let us forget photolysis for laziness. Most of the water we produce is from metabolism, the oxygen from breathing and the hydrogen from biomolecules. (There are desert animals that can live on this water only.) That water is transported out several ways (breathing et cetera).

      Using humans as model organism, reasonably roughly 1 dm^3/(100 kg cells*day) or ~ 3*10^-3 m^3/(kg biomass*year).

      Earth biomass is ~ 1000 billion tonnes C including bacteria or ~ 10^12 kg, so the biological water cycling is ~ 3*10^9 m^3 or ~ 3 km^3 each year.

      So at least ~ 10^-7 of the total water mass is recycled every year. A sanity check is the biomass link that says ~ 20 % biomass is recycled every year, which roughly accords with the water production value.

      The atmospheric loss to space, mainly photolyzed hydrogen atoms, is obviously much less since Earth is ~ 5*10^9 years old and we have had similar volumed oceans the whole time.

  18. Reminds me of a post from 2010, which has an image with two water spheres instead of one.
    One is salt water, one is fresh water. The fresh water sphere is just a dot. Shows even better how little fresh water we have:

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