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I am curious about how various estimates can divert. The first picture is taken from a recent publication of VisualCapitalist https://www.visualcapitalist.com/sp/hf01-visualizing-all-of-the-worlds-water/

The second picture can be found in an older Soviet book by Larionov published in 1989, the book's called "Amusing hydrogeology".

As can be seen, the estimates of the groundwater are rather different. The Russian book puts its estimate at roughly the same level with oceans, while Visual Capitalist estimated it at the same level with glaciers.

So the question remains, what estimate is more valid?

enter image description here enter image description here

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    $\begingroup$ Don't forget the mantle! Estimates vary, but there could be a few oceans down there (trapped in mineral structures though, not literal oceans). $\endgroup$ Commented Mar 21 at 20:56

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The accompanying text to the second image states "The second place is occupied by the mass of invisible water in the earth's crust and partly in the mantle. Here it contains about 1300 million km³." The key statement is that the estimate includes water in the mantle, as well as the crust. The smaller figure, of 23 million km³, quoted in the first image, is an estimate of groundwater that might be considered to be in active circulation, albeit in some cases at millennial timescales. Estimates of groundwater volume can vary considerably, depending on assumptions about depth, movement and porosity etc. Groundwater volume is often quoted as high as 60 million km³, twice the volume of glaciers. The amount that might be actually accessible to ecosystems or abstraction is likely to be at least an order of magnitude lower, maybe as low as or as low as 4 million km³.

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