Measuring Earth’s Freshwater Reserves

Jeremiah Z.
7 min readMay 12, 2021

Three hundred twenty-six million cubic miles of endless blue sea occupy the expanse between our seven continents, making up 70% of the earth’s surface (Bureau of Reclamation, 2017).

With merely 5% of the ocean floor having been discovered and mapped, and with the deepest part reaching almost 7 miles, water seems to be as abundant as it is ominous.

Yet, if consumed, it wouldn’t take much of the mineral-rich ocean to dehydrate a human being. The amount of sodium in seawater is much more concentrated than what the body can safely process, requiring more water as salt is consumed. Eventually, death would come as a result of dehydration without ever having the thirst quenched (Ocean Service).

Of the waters occupying 70% of the earth’s surface, only 3% is considered freshwater. Most of this freshwater reserve is inaccessible to humans — locked up in polar ice caps or stored too far underneath the earth’s surface to be extracted. Furthermore, much of the freshwater that is accessible has become highly polluted.

This leaves us with roughly 0.4% of the earth’s water, which is usable and drinkable to be shared among the 7 billion of its inhabitants (World Atlas, 2018).

And still, much of this 0.4% is hard to get to. Most of it flows through underground aquifers, which can be accessed by digging wells; the rest are found in rivers and streams, which we refer to as surface water. Much of the global population is hard-stricken, having access to such a small percentage of freshwater on the earth’s surface (Perlman, 2016).

The United States Geological Survey provides a visual illustration (represented in spheres) as to the amount of available water in comparison to the size of the earth.


The largest sphere represents all of the water on earth (oceans, ice caps, lakes, rivers, groundwater) and has a volume of 332,500,000 cubic miles.

The second-largest sphere, with a volume of 2,551,100 cubic miles, represents the earth’s freshwater supply in liquid form. 99% of the liquid freshwater is groundwater, much of which is far too deep to be accessible.

The remainder of the earth’s freshwater exists in lakes and rivers, represented by the tiniest sphere, with a volume of 22,339 cubic miles (Perlman, 2016).

Since surface water is easier to reach, it’s become the most common way for humans to access clean water. Globally, we use about 321 billion gallons of surface water and about 77 billion gallons of groundwater per day. Contamination of these water supplies is a problem that further limits availability (Groundwater Association, 2012).

Surface Water

Surface water is any body of water that remains on the earth’s surface, including lakes, rivers, streams, and reservoirs. 80% of the world’s daily water usage comes from surface water, making up most of the water used for irrigation and public supply.

Oceans are the world’s largest source of surface water and makeup 97% of it. However, its high salinity makes it unusable for humans (Postel, 2010).

The earth’s surface waters travel through a complex flowing river and stream network. Rivers can obtain their water from two sources: base flow and runoff. Base flow is when the river collects its water from water-saturated areas in the ground, adding to its volume. Runoff is when the force of gravity naturally pulls water downhill from higher to lower altitudes. They usually start as small creeks in the mountains and then gradually merge with larger streams as they flow downward, eventually forming large rivers that empty out into the ocean.


Groundwater is the water beneath the earth’s surface that is at 100% saturation. Anything less than 100% is considered a soil mixture. 98% of the earth’s freshwater is indeed groundwater, and it is about 60 times more plentiful than surface water.

Groundwater travels through holes and cracks in the bedrock. The amount of rock space and the ability for water to travel through it is known as porosity and permeability. Rock with high porosity and permeability, through which water can travel quickly, is known as an aquifer. An aquifer with high pressure can cause groundwater to rise to the surface once a well has been dug (Groundwater Association, 2012).

The Hydrologic Cycle

Water takes the form of liquid, gas, and solids and cycles through these forms in what is known as the earth’s hydrologic cycle. When water evaporates, liquid molecules become gas molecules as they rise through the atmosphere.

Condensation begins when the moisture from these gas molecules becomes so great that they fall back to earth in the form of precipitation. Because evaporation, condensation, and precipitation have essentially “distilled” the water, it is considered clean before it hits the ground.

When the precipitation hits the ground, it collects into aquifers, rivers, or lakes, ready to be used again. Glaciers and icecaps cover 10% of the world's mass and exist primarily in Greenland and Antarctica. They are the storehouses for the world’s freshwater.

Water Conflict

There are 263 rivers and countless aquifers worldwide, crossing or demarcating geopolitical boundaries. The Atlas of International Freshwater Agreement states that 90 percent of the world’s countries share these water sources with at least one or two other governing bodies. The atrocities in Darfur are an example of conflict resulting from clean water shortages.

  • Violence erupted in 1992 over a dispute between Uzbekistan and Turkmenistan regarding the contested Tyuyamuyun reservoir. It continues to be a highly disputed water source in the region today (Factbook).
  • In 2010, dozens of people were killed in Pakistan’s tribal region due to a water dispute which lasted over two weeks. According to a senior government official in the Kurram district, which borders Afghanistan, the Mangal tribe stopped water irrigation on lands belonging to the Tori tribe. In total, 116 people were killed, and 165 were injured (CNN, 2010).
  • Four farmers were hacked to death in northeast Tanzania over the disputed Pangani River Basin in 2013 (Factbook).
  • In 2016, 18 people were killed, and 200 more were injured when the Indian Army clashed with economic protestors surrounding the highly-contested Munak canal, a water source that supplies New Dehli with three-fifths of its freshwater supply (Factbook).
  • The drought-stricken conditions of major parts of Somalia often force herders to sell more of their livestock than they can afford to make a living with. This lack of economic stability fuels recruitment appeals with militant groups such as Al Shabaab, which provide cash incentives and other benefits to their soldiers. Other illicit activities, such as pirating and livestock raiding, are seen as reasonable alternatives to the declining stability of animal herding (Factbook).

Change is needed

Water is finite. The amount of water circulating through the earth’s hydrologic cycle is the same amount that has been there since the earth’s beginning, not a drop more or less.

What has changed is the number of people living on Earth and, thus, the amount of drinkable water required for human sustenance. The United Nations reports that in the last century alone, water consumption has grown at more than twice the rate of population increase.

70% of the earth is covered in water, yet only 3% of it is fresh, and most of it is locked away in glaciers and polar ice caps. That leaves us with 0.4% of the earth’s water, in the form of rivers and underground aquifers, to try to utilize for our consumption and societal development. It is no wonder that in developing regions where clean water sources cross national boundaries, it often finds itself in conflict among those trying to secure a means to a healthy living.

With humans being made up of 60% water, our natural instinct might be to fight for it. But by collaborating to find ways to access the untapped groundwater beneath us, helping to conserve clean water use, and preventing further pollution of our clean water sources, it is possible for all peoples to have access to clean water.


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CNN. (2010, September). Water conflict in Pakistan’s tribal region leaves dozens dead. Retrieved from

Factbook. (n.d.). Mapping environmental conflicts and cooperation. Retrieved from

Groundwater Association. (2012, September). Information on Earth’s water — National Groundwater Association. Retrieved from

National Geographic. (2017, January 27). Competing for Clean Water Has Led to a Crisis. Retrieved from

Ocean Service. (n.d.). Can humans drink seawater? Retrieved from

Perlman, H. (2016, December 2). Where is Earth’s water? USGS Water-Science School. Retrieved from

Perlman, H. (2016, December 2). How Much Water is on and in the Earth. Retrieved from

Postel, S. (2010, June). How Much Longer Until We Run Out of Enough Drinkable Water? Retrieved from

Shahan, Z. (2017, October 24). How Much Clean Water is Available for Human Use? Retrieved from

United Nations. (2007). Water scarcity. Retrieved from

World Atlas. (2018, February 14). What Percentage of the Earth’s Water Is Drinkable? Retrieved from



Jeremiah Z.

Write about: mental health, mental freedom, self-sufficient living, water purification, jiu-jitsu, communications, graphic design, generative AI art, poetry