Water, we talk about it often on consoGlobe.com, from the angle of water savings or pollution. But many of you have asked us about the stakes: how much water is on Earth? Who uses the most? In short, it was time to take stock of Earth’s water, starting with the fundamental question about the origin and quantity of water on Earth.
Water in all its states on the blue planet
H2O, water, so common, so ordinary, is present everywhere: seas, oceans, groundwater and aquifers, glaciers and polar caps, rivers and streams.
Water is everywhere and foremost in the oceans, which cover more than 70%, i.e., 361 million of the 510 million km2 of the Earth’s surface. In short, next to the bowling ball that is Earth (the Earth’s diameter is 12,756 km), the water on Earth, if isolated, would form a small sphere 1,385 km in diameter.
The Earth’s atmosphere becomes less dense with altitude. In other words, if water on Earth is not rare on the human scale, it is on a geological scale. It represents only a tiny, thin film on the great sphere that is our planet.
The origin of water on Earth
The amount of water has not increased since its appearance on Earth, about 3.4 billion years ago. At the origin, during its formation, the Earth was an arid planet, and waterless.
Nevertheless, around 10 million space bodies—asteroids and comets—fell to Earth in the period between 50 and 100 million years after its formation.
These celestial bodies from the Kuiper Belt or the Oort Cloud are typically under 20 km in diameter and composed of about 80% frozen water. These water- and ice-rich asteroids could have supplied Earth with its water.
There is debate about the origin of gaseous water in the atmosphere. The currently favored hypothesis concerns carbonaceous chondrites carrying water that arrived on Earth at the end of the planet’s accretion.
Water did not come from space
The second hypothesis is that of comets. However, according to the Woods Hole Oceanographic Institution, this hypothesis appears to be false. This research center found that Earth’s water and water in meteorites formed before Earth share the same hydrogen isotope composition. They concluded that water would not have been delivered to Earth by humid comets, but rather was present from the planet’s formation.
Finally, according to the degassing theory, water would have been present in gaseous form in Earth’s various envelopes at the planet’s creation, 4.5 billion years ago.
In any case, about half of the water is infiltrated into the rocky mantle where it remains, and the other half is at the surface. This water gave rise to plate tectonics, making the mantle mobile. That had a major impact on the evolution of life on Earth.
Today, the majority of our freshwater lies beneath our feet in aquifers of varying depths. These aquifers, fed by precipitation that infiltrates through rocks, gravel, or porous sands, are increasingly used.
Where is the water on Earth?
The largest pools of water are of course the oceans and seas, with 1,320 billion km3.
Next, about 24 million km3 are found in the polar ice caps (Greenland and Antarctica), glaciers, and permanent snow.
Then, almost as much water sits in the subsurface and in the Earth’s crust. Other stocks of water are listed in decreasing order as follows:
- the permafrost ice and hydrolaccolites;
- lakes;
- soil moisture;
- atmospheric moisture;
- marshes;
- rivers: worldwide there are about 250 aquifers or international rivers that are potential sources of diplomatic tension, especially in a context of water scarcity;
- green water – that is, water contained in biomass. Green water is all the water contained in plants and living organisms. Green water accounts for two-thirds of Earth’s total water resources, allocated across three uses: agriculture (86%), industry (9%), and domestic water (6%). This water imprisoned in living beings is essential to life: it is estimated that living beings on Earth contain a little over 1,100 km3 of this biological water.
- 1,320,000,000 km3 of saline water (97.2% of the total) are in the oceans.
- 25,000,000 km3 (1.8%) are in the glaciers and ice caps.
- 13,000,000 km3 (0.9%) are underground waters.
- 250,000 km3 (0.02%) of freshwater in lakes, inland seas and rivers.
- A vast mass of 12,900 km^3 of water is present in the atmosphere. Only 2% of this 12,900 km^3 of water in the atmosphere exists in condensed form (clouds); the rest is diffuse, present as water vapor. The water vapor percentage in the atmosphere is small: 0 to 4% of its composition. All together, it represents only 0.001% of the planet’s water.
| Water source | Volume of water (km³) | % of freshwater | % of total water | |
| Oceans, seas & bays | 1.338.000.000 | — | 96,5 % | |
| Calottes glaciaires, glaciers et neiges éternelles | 24.064.000 | 68,7 % | 1,74 % | |
| Eau souterraine | 23.400.000 | — | 1,7 % | |
| – douce | 10.530.000 | 30,1 % | 0,76 % | |
| – saline | 12.870.000 | — | 0,94 % | |
| Humidité du sol | 16,5 | 0,05 % | 0,001 % | |
| Hydrolaccolithe & pergélisol | 300 | 0,86 % | 0,022 % | |
| Lacs | 176,4 | — | 0,013 % | |
| – d’eau douce | 91 | 0,26 % | 0,007 % | |
| – d’eau saline | 85,4 | — | 0,006 % | |
| Atmosphère | 12,9 | 0,04 % | 0,001 % | |
| Eau marécageuse | 11,47 | 0,03 % | 0,0008 % | |
| Rivières | 2,12 | 0,006 % | 0,0002 % | |
| Eau biologique | 1,12 | 0,003 % | 0,0001 % | |
| Total | 1.386.000.000 | – | 100 % | |
Source : Gleick, P. H., 1996 : Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp.817-823. |
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Freshwater on Earth
Of the 3% freshwater, 2.1% (i.e., 60% of the total freshwater) is frozen around the poles, in inland ice or in mountain glaciers and permanent snow. There is thus 40% of unfrozen freshwater.
Freshwater therefore accounts for barely 3% of Earth’s total water, i.e., about 35 million km^3 of freshwater, but nearly 69.5% is in ice and 30% underground. In short, a large portion of water is not directly usable by humanity. Surface freshwater sources, such as rivers and lakes, total 93,100 km^3, which represents less than 1% of the total water quantity.
How much freshwater usable by humans?
Groundwater, freshwater stored in surface rivers, aquifers, as well as surface water bodies and in the atmosphere, represent the accessible freshwater resource.
There are 12,500 km^3 of freshwater available on Earth in the form of rivers, lakes, etc., and even more water in the atmosphere (12,900 km^3).
Blue water
What is called blue water is all the water circulating in rivers and lakes. Blue water is captured in groundwater and then distributed. Agricultural uses account for 49% of blue water usage.
Overall, 99.1% of the Earth’s total freshwater is not directly usable. In other words, the readily accessible and directly usable water accounts for only a small share:
- 0.9% of the freshwater stock is found in unsalted lakes and swamps, rivers and streams (the five largest rivers account for 27% of surface waters), and mostly in groundwater.
- 0.3% of Earth’s water is freshwater usable by humans.
- 0.0001% of Earth’s water is available AND potable.
Water in soils and subsoils
- Around 2,200 km3 of freshwater on Earth flows through soils and feeds subterranean reservoirs. Note that across the planet, the level of groundwater reserves declines by about one meter per year.
- Except for glaciers, there is 100 times more freshwater beneath the surface than above it.
Who has access to water?
According to the UN, 89% of the human population has access to drinking water, i.e., 6.1 billion people; a rate higher than the Millennium Development Goals targeted for 2015 (88%).
1.7 billion people, or a quarter of the world’s population, live in regions where groundwater reserves are being overexploited.
In the least developed countries (LDCs), 97% of residents do not have access to piped drinking water, and 14% drink surface waters (ponds, rivers, lakes, …).
61% of Sub-Saharan Africa’s inhabitants have access to potable water thanks to connections to a distribution network or to a well. This rate is 90% in Latin America, North Africa, the Caribbean, and much of Asia.
This precious resource is nonetheless used predominantly for non-human consumption: water is used 70% for irrigation, 22% for industry, and 8% for domestic use.
