The ground stores huge amounts of water and it exists to some degree no matter where on Earth you are. Lucky for people, in many places the water exists in quantities and at depths that wells can be drilled into the water-bearing aquifers and withdrawn to server the many needs people have.
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Water cycle components » Atmosphere · Condensation · Evaporation · Evapotranspiration · Freshwater lakes and rivers · Groundwater flow · Groundwater storage · Ice and snow · Infiltration · Oceans · Precipitation · Snowmelt · Springs · Streamflow · Sublimation · Surface runoff
There's a whole lot of water beneath your feet
Large amounts of water are stored in the ground. The water is still moving, possibly very slowly, and it is still part of the water cycle. Most of the water in the ground comes from precipitation that infiltrates downward from the land surface. The upper layer of the soil is the unsaturated zone, where water is present in varying amounts that change over time, but does not saturate the soil. Below this layer is the saturated zone, called groundwater, where liquid water is stored in all the pores, cracks, and spaces between rock particles. The term aquifer refers to water-bearing foundations or rocks that can hold large amounts of water. Aquifers are a huge storehouse of Earth's water and people all over the world depend on groundwater in their daily lives.
The top of the surface where groundwater occurs is called the water table. In the diagram, you can see how the ground below the water table is saturated with water (the saturated zone). Aquifers are replenished by the seepage of precipitation that falls on the land, but there are many geologic, meteorologic, topographic, and human factors that determine the extent and rate to which aquifers are refilled with water. Rocks have different porosity and permeability characteristics, which means that water does not move around the same way in all rocks. Thus, the characteristics of groundwater recharge vary all over the world.
Credit: Howard Perlman, USGS
To find water underground, look under the (water) table
This beach photo is a great way to illustrate the concept of how the ground is saturated with water at a certain depth if it is permeable enough to allow water to move through it. The top of the pool of water in this hole is the water table. The breaking waves of the ocean are just beyond this hole, and the water level in the hole is the same as the level of the ocean. Of course, the water level here changes by the minute due to the movement of the tides, and as the tide goes up and down, the water level in the hole moves, too. Just as with this hole, the level of the water table is affected by other environmental conditions.
The hole in the photo to the right is like a dug well used to access groundwater, probably saline in this case. But if this was freshwater, people could grab a bucket and supply themselves with the water they need to live their daily lives. This might sound familiar: If you took a bucket and tried to empty this hole, it would refill immediately. Why is that? It's because the sand is so permeable that water flows easily through it, meaning our "well" is very "high-yielding" (too bad the water is saline). To access freshwater, people must drill wells deep enough to tap into an aquifer. The well might have to be dozens or thousands of feet deep. But the concept is the same as the "well" in the photo — we must access the water in the saturated zone where the voids in the rock are full of water.
Pumping can affect the level of the water table
In an aquifer, the soil and rock are saturated with water. If the aquifer is shallow enough and permeable enough to allow water to move through it at a rapid-enough rate, then people can drill wells into it and withdraw water. The level of the water table can naturally change over time due to changes in weather cycles and precipitation patterns, streamflow and geologic changes, and even human-induced changes, such as the increase in impervious surfaces, such as roads and paved areas, on the landscape.
The pumping of wells can have a great deal of influence on water levels below ground, especially in the vicinity of the well, as this diagram shows. Depending on geologic and hydrologic conditions of the aquifer, the impact on the level of the water table can be short-lived or last for decades, and the water level can fall a small amount or many hundreds of feet. Excessive pumping can lower the water table so much that the wells no longer supply water—they can "go dry."
Groundwater and global water distribution
As these charts show, even though the amount of water locked up in groundwater is a small percentage of all of Earth's water, it represents a large percentage of total freshwater on Earth. About 1.7 percent of all of Earth's water is groundwater and about 30.1 percent of freshwater on Earth occurs as groundwater. As the bar chart shows, about 5,614,000 cubic miles (mi3), or 23,400,000 cubic kilometers (km3), of groundwater exist on Earth. About 54 percent is saline, with the remaining 2,526,000 mi3 (10,530,000 km3) , about 46 percent, being freshwater.
Water in aquifers below the oceans is generally saline, while the water below the land surfaces (where freshwater, which fell as precipitation, infiltrates into the ground) is generally freshwater. There is a stable transition zone that separates saline water and freshwater below ground. It is fortunate for us that the relatively shallow aquifers that people tap with wells contain freshwater, since if we tried to irrigate crops with saline water, they would not grow well.

Water source | Water volume, in cubic miles |
Water volume, in cubic kilometers |
Percent of total water | Percent of total freshwater |
---|---|---|---|---|
Fresh groundwater | 2,526,000 | 10,530,000 | 0.8% | 30.1% |
Groundwater | 5,614,000 | 23,400,000 | 1.7% | -- |
Total global water | 332,500,000 | 1,386,000,000 | -- | -- |
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.
Do you think you know about groundwater?
Take our Groundwater true/false quiz.
Sources and more information:
More topics and other components of the water cycle:
Precipitation and the Water Cycle
Streamflow and the Water Cycle
Snowmelt Runoff and the Water Cycle
Evaporation and the Water Cycle
The Atmosphere and the Water Cycle
Condensation and the Water Cycle
Infiltration and the Water Cycle
Sublimation and the Water Cycle
Surface Runoff and the Water Cycle
Ice, Snow, and Glaciers and the Water Cycle
Groundwater Flow and the Water Cycle
Groundwater Storage and the Water Cycle
Below are publications associated with the water cycle.
Ground water and surface water: A single resource
- Overview
The ground stores huge amounts of water and it exists to some degree no matter where on Earth you are. Lucky for people, in many places the water exists in quantities and at depths that wells can be drilled into the water-bearing aquifers and withdrawn to server the many needs people have.
• Water Science School HOME • Groundwater topics • The Water Cycle •
Water cycle components » Atmosphere · Condensation · Evaporation · Evapotranspiration · Freshwater lakes and rivers · Groundwater flow · Groundwater storage · Ice and snow · Infiltration · Oceans · Precipitation · Snowmelt · Springs · Streamflow · Sublimation · Surface runoff
There's a whole lot of water beneath your feet
Large amounts of water are stored in the ground. The water is still moving, possibly very slowly, and it is still part of the water cycle. Most of the water in the ground comes from precipitation that infiltrates downward from the land surface. The upper layer of the soil is the unsaturated zone, where water is present in varying amounts that change over time, but does not saturate the soil. Below this layer is the saturated zone, called groundwater, where liquid water is stored in all the pores, cracks, and spaces between rock particles. The term aquifer refers to water-bearing foundations or rocks that can hold large amounts of water. Aquifers are a huge storehouse of Earth's water and people all over the world depend on groundwater in their daily lives.
The top of the surface where groundwater occurs is called the water table. In the diagram, you can see how the ground below the water table is saturated with water (the saturated zone). Aquifers are replenished by the seepage of precipitation that falls on the land, but there are many geologic, meteorologic, topographic, and human factors that determine the extent and rate to which aquifers are refilled with water. Rocks have different porosity and permeability characteristics, which means that water does not move around the same way in all rocks. Thus, the characteristics of groundwater recharge vary all over the world.
We dug this hole in the sand on the beach, right next to the ocean. This hole serves as an excellent example of a dug well used to access groundwater. The water that is visible represents the level of the water table, which is at sea level.
Credit: Howard Perlman, USGSTo find water underground, look under the (water) table
This beach photo is a great way to illustrate the concept of how the ground is saturated with water at a certain depth if it is permeable enough to allow water to move through it. The top of the pool of water in this hole is the water table. The breaking waves of the ocean are just beyond this hole, and the water level in the hole is the same as the level of the ocean. Of course, the water level here changes by the minute due to the movement of the tides, and as the tide goes up and down, the water level in the hole moves, too. Just as with this hole, the level of the water table is affected by other environmental conditions.
The hole in the photo to the right is like a dug well used to access groundwater, probably saline in this case. But if this was freshwater, people could grab a bucket and supply themselves with the water they need to live their daily lives. This might sound familiar: If you took a bucket and tried to empty this hole, it would refill immediately. Why is that? It's because the sand is so permeable that water flows easily through it, meaning our "well" is very "high-yielding" (too bad the water is saline). To access freshwater, people must drill wells deep enough to tap into an aquifer. The well might have to be dozens or thousands of feet deep. But the concept is the same as the "well" in the photo — we must access the water in the saturated zone where the voids in the rock are full of water.
Pumping can affect the level of the water table
In an aquifer, the soil and rock are saturated with water. If the aquifer is shallow enough and permeable enough to allow water to move through it at a rapid-enough rate, then people can drill wells into it and withdraw water. The level of the water table can naturally change over time due to changes in weather cycles and precipitation patterns, streamflow and geologic changes, and even human-induced changes, such as the increase in impervious surfaces, such as roads and paved areas, on the landscape.
The pumping of wells can have a great deal of influence on water levels below ground, especially in the vicinity of the well, as this diagram shows. Depending on geologic and hydrologic conditions of the aquifer, the impact on the level of the water table can be short-lived or last for decades, and the water level can fall a small amount or many hundreds of feet. Excessive pumping can lower the water table so much that the wells no longer supply water—they can "go dry."
Groundwater and global water distribution
As these charts show, even though the amount of water locked up in groundwater is a small percentage of all of Earth's water, it represents a large percentage of total freshwater on Earth. About 1.7 percent of all of Earth's water is groundwater and about 30.1 percent of freshwater on Earth occurs as groundwater. As the bar chart shows, about 5,614,000 cubic miles (mi3), or 23,400,000 cubic kilometers (km3), of groundwater exist on Earth. About 54 percent is saline, with the remaining 2,526,000 mi3 (10,530,000 km3) , about 46 percent, being freshwater.
Water in aquifers below the oceans is generally saline, while the water below the land surfaces (where freshwater, which fell as precipitation, infiltrates into the ground) is generally freshwater. There is a stable transition zone that separates saline water and freshwater below ground. It is fortunate for us that the relatively shallow aquifers that people tap with wells contain freshwater, since if we tried to irrigate crops with saline water, they would not grow well.
Sources/Usage: Public Domain. Visit Media to see details.One estimate of global water distribution Water source Water volume,
in cubic milesWater volume,
in cubic kilometersPercent of total water Percent of total freshwater Fresh groundwater 2,526,000 10,530,000 0.8% 30.1% Groundwater 5,614,000 23,400,000 1.7% -- Total global water 332,500,000 1,386,000,000 -- -- 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.
Do you think you know about groundwater?
Take our Groundwater true/false quiz.Sources and more information:
- Science
More topics and other components of the water cycle:
Filter Total Items: 15Precipitation and the Water Cycle
Precipitation is water released from clouds in the form of rain, freezing rain, sleet, snow, or hail. Precipitation is the main way atmospheric water returns to the surface of the Earth. Most precipitation falls as rain.Streamflow and the Water Cycle
What is streamflow? How do streams get their water? To learn about streamflow and its role in the water cycle, continue reading.Snowmelt Runoff and the Water Cycle
Perhaps you've never seen snow. Or, perhaps you built a snowman this very afternoon and perhaps you saw your snowman begin to melt. Regardless of your experience with snow and associated snowmelt, runoff from snowmelt is an important component of the global movement of water, possibly even if you live where it never snows. Note: This section of the Water Science School discusses the Earth's...Evaporation and the Water Cycle
Evaporation is the process that changes liquid water to gaseous water (water vapor). Water moves from the Earth’s surface to the atmosphere via evaporation.The Atmosphere and the Water Cycle
The atmosphere is the superhighway in the sky that moves water everywhere over the Earth. Water at the Earth's surface evaporates into water vapor, then rises up into the sky to become part of a cloud which will float off with the winds, eventually releasing water back to Earth as precipitation.Condensation and the Water Cycle
Condensation is the process of gaseous water (water vapor) turning into liquid water. Have you ever seen water on the outside of a cold glass on a humid day? That’s condensation.Infiltration and the Water Cycle
You can't see it, but a large portion of the world's freshwater lies underground. It may all start as precipitation, but through infiltration and seepage, water soaks into the ground in vast amounts. Water in the ground keeps all plant life alive and serves peoples' needs, too.Sublimation and the Water Cycle
Solid, liquid, and gas - the three states of water. We see water freeze, transforming into a solid form such as ice, and we see water evaporate, turning into gas, but... have you ever seen ice transform directly to gas? This process is called sublimation and you can read all about it below.Surface Runoff and the Water Cycle
When water "runs off" the land surface, that’s runoff! Due to gravity, the water you wash your car with runs down the driveway as you work, and rain runs downhill. Runoff is an important component of the water cycle.Ice, Snow, and Glaciers and the Water Cycle
The water stored in ice and glaciers moves slowly through are part of the water cycle, even though the water in them moves very slowly. Did you know? Ice caps influence the weather, too. The color white reflects sunlight (heat) more than darker colors, and as ice is so white, sunlight is reflected back out to the sky, which helps to create weather patterns.Groundwater Flow and the Water Cycle
Yes, water below your feet is moving all the time, but not like rivers flowing below ground. It's more like water in a sponge. Gravity and pressure move water downward and sideways underground through spaces between rocks. Eventually it emerges back to the land surface, into rivers, and into the oceans to keep the water cycle going.Groundwater Storage and the Water Cycle
The ground stores huge amounts of water and it exists to some degree no matter where on Earth you are. Lucky for people, in many places the water exists in quantities and at depths that wells can be drilled into the water-bearing aquifers and withdrawn to server the many needs people have. - Publications
Below are publications associated with the water cycle.
Ground water and surface water: A single resource
The importance of considering ground water and surface water as a single resource has become increasingly evident. Issues related to water supply, water quality, and degradation of aquatic environments are reported on frequently. The interaction of ground water and surface water has been shown to be a significant concern in many of these issues. Contaminated aquifers that discharge to streams canAuthorsThomas C. Winter, Judson W. Harvey, O. Lehn Franke, William M. Alley