The importance of water cannot be understated. We use it for food preparation, drinking, cleaning, irrigation, transport, recreation, and industrial purposes. Water is arguably the most important natural resource and it can be classified into two broad categories – fresh and salty water. Freshwater refers to water that has less than 1% dissolved salts.
Due to climate change, some water sources that have previously been readily available and accessible have become unreliable, fluctuating, diminishing, or even wiped out. In this blog post, we will have a look at the main sources of water.
There are 10 main sources of water:
- Extraterrestrial sources
- The ocean and seas
- Atmospheric sources
- Glaciers and icecaps
- Underground sources
- Lakes, dams, and reservoirs
- Ponds, marshes, and swamps
- Rivers and streams
- Municipal sources
- Other alternative sources
Let’s have a look at each of these sources in greater detail below.
1. Extraterrestrial sources (comets, meteors, and asteroids)
According to planetary scientists, most of the water found on planet Earth today may have originated from outer space billions of years ago. Recent scientific models indicate that the sun had a role in its formation through the interaction of solar winds with dust from C-type asteroids that originate from beyond our solar system.
These asteroids are the sources of carbonaceous chondrite meteorites that contain high quantities of water-rich minerals, and they often came into collision with our planet during its formative years.
In addition, silicate-rich minerals found in other types of chondrite asteroids (S-type) have shown signs of water. Previously, irradiation of such silicate rocks by solar winds had been put forward as a probable theory for the origin of the water. It has come to be proven experimentally that such minerals can indeed react with hydrogen ions to form water.
These enstatite chondrites (silicate rocks) from comets and asteroids were then integrated into the planet, resulting in the surface water found in the oceans and the atmospheric water vapor.
2. Oceans and Seas
Oceans
An ocean is, by definition, a continuous body of salty water confined within a large basin on the surface of Earth surface.
Oceans are the features that make our planet the typical blue planet it is, covering over 70% of the entire surface and reaching depths greater than 10 kilometers at their deepest points. They are the largest source of surface water serving continental landmasses. 97.957% of the water on the planet is salty and comes mainly from the oceans.
Generally, there is only one ocean on the whole planet. However, it is subdivided into five different oceans, named the Pacific, Atlantic, Indian, Southern, and Arctic oceans, through arbitrary boundaries based on the continents that border them and geographical coordinates.
Waters in the different oceans are characteristically the same. They are all salty, with an average salinity of 35 g/L, and have pHs ranging between 7.5 and 8.4. Oceanic water is denser than fresh water and contains all naturally occurring elements as ions.
Seas
They are the second-largest surface water bodies on the planet. Seas are often confused with oceans, and people often use the terms interchangeably to mean the same thing, yet they are different. Whereas oceans separate continents, seas are typically margins of oceans that extend into the continents and are partly enclosed by land.
Seas are smaller subdivisions of the oceans according to historical, political, and even ecological reasons, with their classification and naming changing over time.
There are seven officially recognized seas namely the Indian, North Atlantic, South Atlantic, Arctic, Southern Oceans, North Pacific, and South Pacific seas. Seawater is not different from ocean water.
It is saline with a salt concentration of about 35 parts per thousand, meaning that 2.5% of the sea consists of salts, dissolved organic and inorganic chemicals, atmospheric gases, and other particles.
3. Atmospheric Sources
Although the atmosphere is considered one of the most important water reservoirs of the earth, it does not store water but acts as a pathway along the water cycle. Water gets into the air through evaporation from surface water bodies which account for 90% of the water in the atmosphere, and transpiration by plants which contributes 10%.
The heat from the sun turns liquid water in the ocean, lakes, rivers, and the soil into vapor, which rises into the air by convectional currents. As the water vapor particles cool, they form clouds, condensing into liquid water and falling back to the earth’s surface as rain or precipitation.
In this way, surface water sources get restored, and the process repeats in what has become known as the hydrological cycle.
Clouds, which are the best evidence of water in the atmosphere, carry trillions of tiny droplets and vary in color depending on how light reflects from them. There are approximately 12.9 quadrillion liters of water in the atmosphere at any given time, accounting for only 0.001% of the total volume of water on earth. Rainwater is a suitable seasonal water source for households and small communities without other sources.
Unless polluted by toxic gases, smoke, and dust particles, water from the atmosphere is usually soft, clean, pure, and fresh. Pollutants in the air can make rainwater acidic or hard by lowering or raising its pH.
Water harvested from rainfall may also get contaminated during the harvesting process, by dirty rooftops or surfaces on which it lands, by gutters, pipes, or storage containers, and may need to be filtered before being used for drinking.
Because rainwater is generally soft, it does not cause scale in cooking appliances, boilers, or washing machines. It also lathers well with soap, so it is the most preferred for domestic use. Additionally, little or no purification and subsequent distribution is needed, making it the cheapest of all water sources, as long as the proper surfaces for collection are in place.
4. Glaciers and Icecaps
Glaciers and icecaps are seasonal ice features that store freshwater at higher altitudes and latitudes. They are reliable water sources in many mountainous areas that experience seasonal rainfall. Glaciers and ice caps account for 1.64% of the total water content, while glacial drainage features span 26% of the earth’s surface.
Mountains are the biggest Water Towers in the World, providing water from melting glaciers or ice caps and relief rainfall to at least a third of the world’s population.
Although seasonal, meltwater runoff from mountains flows downstream and contributes to the availability of freshwater used in irrigation, hydropower, and ecosystems during hot seasons.
Mountain and arctic glaciers globally are continuing to melt by between 230 and 260 gigatonnes per year because of global warming and climate change, resulting in an extraordinary rise in sea levels of up to 0.67 mm. Existent glaciers were formed by snowfall over thousands of years but are now receding because of climate change.
Glacier water is generally salt and mineral-free. However, since moving glacier grinds and erodes surface rocks through abrasion, downstream glacial lakes may contain levels of mineral salts not present upstream.
5. Ground Water Aquifers
Groundwater reservoirs contain 1.69% (approximately 23,400,000 cubic kilometers) of the global water volume. They form when water from rainfall, oceans, seas, lakes, rivers, streams, and dams saturate the ground and percolate through cracks and pores into the underground water table.
This water may be fresh or salty depending on the mineral content of the soil and the underground water-bearing rocks called aquifers. Springs, dug-out wells, and drilled boreholes are the main ways of accessing groundwater for use.
Springs
As water flows underground, it may encounter cracks that lead up to the land surface, and if it has sufficient pressure, it can rise through such fissures and emerge as a trickle or a continuously flowing stream known as a spring. Underground water can also expand due to heating by rocks or lava to crate hot springs and geysers that spew hot water to the surface under pressure.
Springs generally occur where aquifers are intersected at or below the water table by hills, escarpment floors, or quarries, especially when the aquifers or water tables fill to overflow after high rainfall. They also occur along mid-ocean rifts in the oceans, seas, and other large water bodies.
The volume of water discharged from a spring depends on the size and number of fissures in the rocks, the pressure of water in the aquifer, the width of the underground water basin, the amount of rainfall, and the local human activities.
Hot springs have high levels of mineral salts and sulfur that cause the coloration of their water. Many springs produce clear water, but some have pigmented waters due to interaction between groundwater and naturally occurring minerals in the rocks, volcanic activity, leaching from the topsoil, or seepage of surface runoff into the aquifer. Springwater usually has the same quality as the local groundwater system.
Although it may appear clear and clean, it may still include germs such as viruses and bacteria and chemical contaminants, making it unsafe to drink.
Drilled wells and boreholes
Wells and boreholes differ in their construction and water levels.
Shallow wells are usually constructed by hand digging, are between four and ten meters deep, and employ relatively simple ways to pump water to the surface. They are a source of limited clean water in many rural communities.
They provide varying quantities and qualities of water according to their geographical locations, depths, the season of the year, amount of rainfall in their localities, the types of pumps used, mineral composition, size, and permeability of the aquifer rocks.
Government regulations require digging wells at certain minimum distances from sewer systems and buildings and that the water that comes from them undergo regular water quality checks.
Boreholes are deeper than wells and are bored using heavy drilling machines to penetrate hard rocks that would otherwise not be dug through by hand. They also use more advanced pumps that are often submerged below the water to bring water to the surface. Typically electric pumps with sufficient horsepower to overcome atmospheric pressure and altitude limitations are used.
Learn more about how to filter well water here!
6. Lakes, reservoirs, and dams
Lakes are the third-largest surface water bodies worldwide but are considered temporary in geological scales. They are found on the mainland of continents within inland basins and can either be stationary or slow-moving, natural or artificial.
Scientists have also discovered some lakes (at least 400) beneath the ice in the arctic. Artificial lakes exist in the form of reservoirs and dams. Lakes are an important source of clean and fresh water that requires very little treatment for use in households, industries, and farms due to their ease of access.
There are an estimated 117 million freshwater and saltwater lakes globally, making up 0.013% of the total water volume. That is about 176.4 quadrillion liters of water, out of which only 20.9% (0.4% of the total water volume) is fresh and the rest salty. Freshwater lakes supply over 98 percent of all the water used worldwide, which constitutes 0.009% of all the liquid water on the planet.
On the other hand, salty lakes and inland seas contribute 0.0075% of all water. The top 40 largest lakes contain approximately 80% (125,000 cubic km) of all the lake waters, while the remaining small lakes, dams, and reservoirs account for only 20%.
Lakes receive water from a combination of rain, rivers, small streams, surface runoff, meltwater, and groundwater. Some have outlets that drain their waters to the ocean or the seas, while others do not. Water levels in lakes vary with the seasons and amounts of rainfall in the catchment areas where their rivers originate. As a result, when humans exploit lakes without regard for the amount of water that flows in or due to high rates of sedimentation, evaporation, pollution, and invasion by aquatic plants from nutrient enrichment, they can dry up over time.
Increased human settlement, urbanization, and industrialization around freshwater lakes have exposed them to pollutants. Therefore it is necessary to treat lake water before ingesting it.
However, in most cases, lakes’ water usually undergoes self-purification by aeration, bio-chemical degradation, sedimentation, and replenishment through inflow and outflow. Lake water is mostly clear, like rainwater, meltwater, and groundwater.
7. Ponds, marshes, and swamps
These are surface water sources that are smaller and shallower than lakes. They may be formed naturally through earth processes like erosion and landslides or artificially through human activities like quarrying, damming, and excavations.
Rain, surface runoff, and diverted rivers can all fill them up. As a result, chemicals and minerals from the soil, such as fertilizers, may concentrate in ponds, marshes, and swamps, supporting the growth of aquatic plants such as grasses, trees, bushes, algae, and a variety of marine animals and microorganisms.
For this reason, drinking water from these sources might not be safe unless it has been filtered. That said, ponds, swamps, and marshes are valuable freshwater sources for most applications like irrigation and fishing.
8. Rivers and streams
Rivers are relatively fast-moving bodies of water that begin as streams in mountainous regions with high rainfall, snowmelt, or springs from underground reservoirs. Most of the freshwater used by humans and animals comes from rivers, which account for 0.0002% of the total water volume (an equivalent of 2.12 quadrillion liters).
Rivers are differentiated from lakes or reservoirs by the rates at which water moves or flows through them. Where a river receives most of its water is known as a catchment area. Those with large catchment areas tend to be permanent rivers with little or no fluctuation in their levels.
The water in rivers, streams, and creeks is supplied to a great extent by rainfall, underground aquifers, ice melt, and surface runoff from the soil. Permanent rivers receive water throughout the year, whereas perennial ones dry up during the dry season and fill up once the rains resume.
Barriers are frequently built across rivers to create artificial lakes that retain water during the rainy season and release it during the dry season to protect downstream towns from seasonal changes in river levels.
Riverbanks can also store significant amounts of water in the soil during heavy rains and floods, which is then slowly released into the river as its level falls. Because rivers absorb runoff and discharges of industrial effluents, they are typically more contaminated than any other source, necessitating thorough treatment before ingestion.
9. Municipal sources
These public water supply facilities or networks include treatment, storage (such as water towers, reservoirs, or tanks), and distribution equipment to distribute treated water to home, institutional, commercial, and industrial users. Around a quarter of a billion people in cities and other urban areas around the globe depend on municipal water sources annually.
In the United States, it is the dominant water source for about 90% of the population.
Governments inspect municipal water suppliers regularly to verify that the water they provide meets the set quality criteria. Water treatment facilities are often designed based on these predetermined quality standards, specific user needs, and the quantities of water in demand.
Fluoride, as a health measure, chlorine, as an antibacterial, and sodium salts, as a water softening agent, are usually combined with water throughout the treatment at rates that are preset not to harm humans, animals, or plants.
In addition, heavy metals, odor-causing organic compounds, and sediments are filtered out at these facilities to ensure that the water reaching consumers is as pure, fresh, clean, and safe as possible. As a result, municipal water sources are often expensive to run but they provide quality water for drinking, cooking, washing, and irrigation of plants without the need for further treatment.
10. Other alternative sources
Volcanic eruptions
Volcanic eruptions can contain as much as 60% water vapor. According to scientific findings, water may have accreted alongside dust during the formation of our planet, as demonstrated by the substance found in volcanic rocks from deep inside the mantle.
Igneous rock magmas contain dissolved carbon dioxide, sulfur dioxide, and water. The amounts of these dissolved gases increase as the pressure rises below the crust rises and diminishes to zero at atmospheric pressure.
About 5% of the weight of igneous magma at a depth of six kilometers below the surface is water. The dissolved water vaporizes and gets separated as the magma moves towards the surface, building enough gas pressure to cause explosive volcanic eruptions that release the water vapor into the atmosphere.
Other studies have shown that water-bearing minerals can be found at depths of between 150km to 660km, giving more weight to the idea that water on the surface may have originated from deep down in the mantle through volcanic activities.
Combustion of fuels
The combustion of fuels such as hydrogen gas and hydrocarbons also produces a small amount of water on the planet. Burning or oxidation of hydrocarbon fuels results in the release of water as a byproduct alongside carbon dioxide. This water, in vapor form, is released into the atmosphere and contributes to the total water volume.
Natural gas is the most widely used hydrocarbon fuel and produces more water per unit than oil, coal, and other natural gas derivatives. Studies have shown that the total amount of water produced in the US yearly from the oxidation of hydrocarbon fuels is more than the water obtained from deep wells within the same duration but significantly less than the volume that gets into the atmosphere through evaporation and transpiration.
Metabolic water
Metabolic water is water formed when food nutrients like proteins, fats, and carbohydrates are burnt down through oxidation in the body tissues of living organisms to produce energy. In addition to the water consumed in food and by drinking, it accounts for a small fraction of the water used by many animals and vital source of water for animals that live in dry areas with scarce water resources.
Camels, kangaroo rats, and migratory birds can safely rely on this water and not have to drink from other sources for long periods.
For example, the approximate metabolic water yield is 1.07 grams per gram of fat, 0.56 grams per gram for glucose carbohydrate, and 0.4 grams for protein. Depending on their diets, mammals obtain about a tenth of their total water intake from the metabolic water source. That is approximately as much as is required to eliminate urea from their systems.
Unlike proteins, which also produce urea, fats and carbohydrates generate more water and energy per gram and per liter of oxygen, helping the body preserve water.
Final Thoughts
The sixth goal of the United Nations Sustainable Development Goals (UNSDGs) recognizes the need to ensure the availability and sustainable management of water and sanitation for all. Before proper actions to use and manage available water resources can be undertaken, the first step in this direction is to identify them.
It is also vital to understand how Climate change and pollution affect the availability and distribution of these resources, resulting in resource fluctuations, socioeconomic upheaval, and poor health consequences.
This post demonstrates how water resources are diverse and widely distributed around the globe, both geographically and over time, as well as the stresses that human populations exert on them through usage and exploitation.
This article is not exhaustive; instead, it attempts to outline where the water on the planet originates from and how it exists. As a precaution, we recommend using a water filter to ensure you only consume purified water. Refer to this article for help in picking the best water filtration system for your unique needs.