How much water is there in total in the world? The total amount of water on Earth is about 1.386 billion cubic kilometers. Of that total amount, about 97% is salt water found in oceans and seas, while just 3% is freshwater. The majority of Earth’s freshwater is locked up in glaciers and ice caps, with only about 1% of all freshwater readily accessible for human use.
Breakdown of Earth’s Water
Here is a breakdown of the total amount of water on Earth:
| Source of Water | Volume (cubic km) | Percent of Total |
|---|---|---|
| Oceans | 1,338,000,000 | 96.5% |
| Ice caps and glaciers | 29,000,000 | 2.1% |
| Groundwater | 9,000,000 | 0.7% |
| Freshwater lakes | 125,000 | 0.01% |
| Inland seas | 85,000 | 0.006% |
| Soil moisture | 20,000 | 0.001% |
| Atmosphere | 14,000 | 0.001% |
| Rivers | 2,250 | 0.0002% |
| Total | 1,386,000,000 | 100% |
As the table shows, oceans contain by far the most water, holding about 96.5% of the total global water reserves. Ice caps and glaciers hold the second largest amount of water. Only a very small fraction of the world’s total water is found in lakes, rivers, groundwater, soil moisture, and the atmosphere.
Oceans
The oceans contain approximately 1,338,000,000 cubic kilometers of water, accounting for over 96% of the water on Earth. The Pacific Ocean is the world’s largest ocean, containing more than half of all ocean water. The Atlantic, Indian, Southern, and Arctic Oceans make up the rest of the global oceanic water.
Ocean water has an average salinity of about 3.5%. This means there are roughly 35 grams of dissolved salts, primarily sodium chloride, per kilogram of seawater. The salinity can vary regionally, such as in areas where freshwater from rivers flows into the ocean. But overall, the oceans have a remarkably constant salinity worldwide.
The tremendous volume of water in the oceans serves as a major reservoir for Earth’s hydrologic cycle. Water evaporates from the ocean surface, condenses into clouds in the atmosphere, and then falls back down to Earth as precipitation. Runoff water makes its way back to the seas and oceans through rivers, streams, and groundwater flow. This continuous cycling of ocean water helps regulate global climates and weather patterns.
Ice Caps and Glaciers
The next largest store of Earth’s water is found in ice caps and glaciers, containing approximately 29,000,000 cubic kilometers. Polar ice caps, like those covering Greenland and Antarctica, account for about 99% of all the glacial ice on the planet. These massive ice sheets can be over a mile thick and contain enormous amounts of frozen freshwater.
There are also many smaller mountain glaciers worldwide, for example in the Alps, Andes, and Himalayas. While small in comparison to the polar ice caps, mountain glaciers are incredibly important sources of water for surrounding communities. Glacier meltwater feeds rivers and streams that local populations often rely on.
Nearly all glacial ice consists of freshwater. If all the land ice on Earth were to suddenly melt, it’s estimated that sea levels could rise by about 66 meters. So ice caps and glaciers represent a massive reservoir of potential sea level rise as the planet continues to warm.
Groundwater
Groundwater is found underground in porous spaces between soil, sand, and rock. It accounts for about 0.7% of the world’s total water, or approximately 9,000,000 cubic kilometers. Aquifers are underground layers of permeable rock that can contain large quantities of groundwater. The largest aquifers are found in sedimentary basins where alternating sandstone and shale layers can trap and hold water.
The total amount of groundwater in the world is highly uncertain. Estimates range anywhere from 5 to 25 million cubic kilometers. This is because it is challenging to precisely measure reserves deep underground across the entire planet. Much of the groundwater in the world is effectively isolated and inaccessible as well. Still, groundwater represents a crucially important source of drinking water across the globe.
Roughly 2 billion people worldwide rely on groundwater for drinking. Groundwater is often cleaner and more protected than surface water sources. But many aquifers are being depleted faster than they are recharged by natural infiltration. Sustainable management of groundwater resources is essential to ensure adequate freshwater reserves for the future.
Freshwater Lakes
Natural lakes contain about 125,000 cubic kilometers of freshwater, or around 0.01% of total global water reserves. The Caspian Sea, located between Eastern Europe and Asia, is by far the largest freshwater lake in the world by volume. It holds over 18,000 cubic miles of water, or about 45% of all lake freshwater on the planet.
Other major lakes include Lake Superior in North America, Lake Victoria and Lake Tanganyika in Africa, and Lake Baikal in Russia. Smaller lakes are found on every continent and play integral roles for their ecosystems. Lakes support myriad aquatic plants and animals, and provide vital freshwater resources for surrounding communities.
But lakes around the world face major threats from pollution, invasive species, and unsustainable water withdrawals. Protecting and restoring lake ecosystems is crucial for supporting biodiversity and ensuring sustainable access to freshwater resources. Healthy lakes are economically and culturally valuable assets for societies worldwide.
Inland Seas
Inland seas are large enclosed bodies of saline water, containing around 85,000 cubic kilometers of water or 0.006% of the global total. The largest inland sea is the Mediterranean Sea between Southern Europe, Africa, and the Middle East. Other significant inland seas include the Caribbean Sea and the South China Sea.
Inland seas connect to the open ocean but are partially surrounded by landmasses. Due to limited water exchange, they tend to have higher salinity than the adjoining ocean. Their coastlines are highly populated, supporting major cities from Barcelona to Shanghai.
Activities like fishing, shipping, tourism, and oil drilling make inland seas economically valuable. But they also suffer from heavy pollution pressures. Protecting these semi-enclosed seas from excessive pollution and overuse presents a major challenge for the coastal nations involved. Wise stewardship is necessary to promote sustainable use of inland seas into the future.
Soil Moisture
It may not seem like it when soils become dry and cracked in the hot summer sun, but soil moisture represents an important reservoir of the global water cycle. Soil can contain up to about 50% water by volume, equivalent to about 20,000 cubic kilometers worldwide or 0.001% of total water. But this soil moisture is constantly gained and lost as water infiltrates into the ground and evaporates back into the atmosphere.
The top few meters of soil across the continents may not seem like much. But this relatively small amount of moisture supports nearly all the terrestrial plant life on land. Soil moisture also replenishes groundwater reserves and feeds stream flow and runoff. So it provides the foundation for most agriculture, forestry, and ecosystems on land.
Climate change is already altering patterns of evaporation and precipitation that control soil moisture. Increased drought risks threaten crop productivity and the health of native vegetation. Better monitoring of soil moisture patterns could help improve climate models and resilience in the face of growing water challenges.
Atmosphere
Roughly 14,000 cubic kilometers of freshwater exists in the atmosphere at any one time, about 0.001% of the total. This represents the gaseous water vapor contained in clouds and humid air. Atmospheric water is in constant motion, circulating globally through the hydrologic cycle.
Water evaporates from the ocean and land surface and enters the atmosphere as water vapor. This invisible water vapor gets transported by winds and air currents worldwide. Air can hold more water vapor at higher temperatures. Eventually the vapor condenses into clouds as liquid droplets or ice particles. Clouds release precipitation as rain, snow, or other forms that replenish water on the land and in the oceans.
Atmospheric water is the ultimate renewable resource. The total amount in the atmosphere remains stable over long time periods. But climate change could alter atmospheric circulation patterns that distribute precipitation regionally. A warmer world would also increase surface evaporation and raise the atmosphere’s capacity to hold moisture. Monitoring atmospheric water is critical for weather forecasting and climate modeling.
Rivers
Rivers transport roughly 2,250 cubic kilometers of water, or around 0.0002% of the global total. But rivers have an outsized impact on the planet relative to their modest volume. They act as the arteries of continental landscapes, carrying rainfall and melting snow and ice down to oceans and inland seas. Rivers drain nearly 75% of the Earth’s land surface.
Major rivers like the Amazon, Nile, and Mississippi carry enormous volumes of water from source to mouth. But rivers come in an amazing diversity of forms worldwide. The Amazon carries 15 times more water than the next largest river, the Congo. Some challenging-to-navigate whitewater rivers descend rapidly through mountain terrain. Other sluggish lowland rivers meander slowly across plains.
Rivers support rich ecosystems, transport sediments, and provide vital renewable freshwater resources for human communities. But rivers also face massive threats from pollution, dams, and water diversions. Sustainably managing the world’s rivers is essential to balance human and environmental needs.
Conclusion
While the total global water supply is practically fixed, how humans use that water is not. With only about 1% readily available as liquid freshwater, pressures on water resources will continue mounting with population growth, rising demand, climate change, and environmental degradation. How societies manage their water will determine the sustainability of humanity in the 21st century and beyond.
Wise stewardship of freshwater resources involves: conserving water; protecting lakes, rivers, aquifers, and wetlands; controlling pollution; increasing water use efficiency; and integrated management across sectors and borders. With holistic water policies and education, we can ensure adequate clean water for nature and humanity far into the future. But neglecting sustainable water management puts the health and prosperity of all life on Earth at risk.