As a non-existent proverb states: "Humans don't live by surface water alone." For thousands of years, people have also relied on groundwater to serve their every need. Groundwater is invaluable for many uses, from irrigation to drinking-water supply. But, you can't see groundwater, so how do water scientists know where it is in order to be able to drill wells and pump it out for use?
• Water Science School HOME • Groundwater topics •
How Do Hydrologists Locate Groundwater?
Using scientific methods to locate water
To locate groundwater accurately and to determine the depth, quantity, and quality of the water, several techniques must be used, and a target area must be thoroughly tested and studied to identify hydrologic and geologic features important to the planning and management of the resource. The landscape may offer clues to the hydrologist about the occurrence of shallow groundwater. Conditions for large quantities of shallow groundwater are more favorable under valleys than under hills. In some regions--in parts of the arid Southwest, for example--the presence of "water-loving" plants, such as cottonwoods or willows, indicates groundwater at shallow to moderate depth. Areas where water is at the surface as springs, seeps, swamps, or lakes reflect the presence of groundwater, although not necessarily in large quantities or of usable quality.
It is difficult to visualize water underground. Some people believe that ground water collects in underground lakes or flows in underground rivers. In fact, ground water is simply the subsurface water that fully saturates pores or cracks in soils and rocks. Groundwater is replenished by precipitation and, depending on the local climate and geology, is unevenly distributed in both quantity and quality. When rain falls or snow melts, some of the water evaporates, some is transpired by plants, some flows overland and collects in streams, and some infiltrates into the pores or cracks of the soil and rocks. The first water that enters the soil replaces water that has been evaporated or used by plants during a preceding dry period. Between the land surface and the aquifer water is a zone that hydrologists call the unsaturated zone. In this unsaturated zone, there usually is at least a little water, mostly in smaller openings of the soil and rock; the larger openings usually contain air instead of water. After a significant rain, the zone may be almost saturated; after a long dry spell, it may be almost dry. Some water is held in the unsaturated zone by adhesion and cohesion, and it will not flow toward or enter a well. Similar forces hold enough water in a wet towel to make it feel damp after it has stopped dripping.
Locating groundwater
Groundwater is simply the subsurface water that fully saturates pores or cracks in soils and rocks. Aquifers are replenished by the seepage of precipitation that falls on the land, although they can be artificially replenished by people, also. There are many geologic, meteorologic, topographic, and human factors that determine the extent and rate to which aquifers are refilled with water.
The landscape offers helpful clues. Shallow ground water is more likely to occur in larger quantities under valleys than under hills, because ground water obeys the law of gravity and flows downward just as surface water does. In arid regions the presence of "water-loving" plants is an indication of ground water at shallow depth. Any area where water shows up at the surface, in springs, seeps, swamps, or lakes, must have some ground water, though not necessarily in large quantity or of usable quality.
Rocks are the most valuable clues of all consolidated formations such as sandstone, limestone, or granite as well as for loose, unconsolidated sediments such as gravel or sand. An "'aquifer" is any body of rock that contains a usable supply of water. A good aquifer must be both porous enough to hold water and permeable enough to allow the continuous recharge of water to a well.
Gravel, sand, sandstone, and limestone are among the best aquifers, but they form only a fraction of the rocks in the Earth's crust. Most rocks are fine grained or otherwise '"tight" and store or carry little water.
As a first step in locating ground water, the hydrologist prepares a geologic map showing where the different kinds of rock come to the land surface. Some of the rocks may be so cracked and broken that they provide good openings to carry water underground. The rocks may be so folded and displaced, however, that it is difficult to trace their location underground.
Next, the hydrologist gathers information on the wells in the area—their locations, the depth to water, the amount of water pumped, and the kinds of rock they penetrate. Because the water-seeker cannot always afford to drill a test hole to obtain information, records of wells already drilled are of great value.
If there are no wells in the area, or not enough information is available on existing ones, the hydrologist may contract with a well driller to put down some test holes. At these holes a pumping or aquifer test will be conducted. These tests indicate the water-bearing properties of the aquifer tapped by the well. From the tests the hydrologist can determine the amount of water moving through the aquifer, the volume of water that can enter the well, and the effect of pumping on the water level of other wells in the area.
For man's use of water, quality is just as important as quantity. The hydrologist will take samples of water from different wells and have them chemically analyzed.
The hydrologist's report and geologic map will show where water can be found, its chemical composition, and in a general way, how much is available. This is the scientific approach used by the U.S. Geological Survey, State resource agencies, and consulting engineers in making their ground-water studies. Information about local ground-water conditions may be found in the offices that the U.S. Geological Survey's Water Resources Division maintains in all 50 States.

Do you think you know about groundwater?
Take our Groundwater true/false quiz, part of our Activity Center.
Sources and more information:
- Appraising the Nation's Ground-Water Resources, USGS General Information publication
Quiz icon made by mynamepong from www.flaticon.com
Want to know more about how hydrologists locate groundwater? Follow me to the Geophysics for USGS Groundwater/Surface Water Interaction Studies website!
Below are other science topics associated with groundwater.
Groundwater Information by Topic
Infiltration and the Water Cycle
Groundwater Quality
Groundwater Flow and the Water Cycle
Groundwater Storage and the Water Cycle
Below are publications associated with groundwater.
A primer on ground water
Ground water and the rural homeowner
- Overview
As a non-existent proverb states: "Humans don't live by surface water alone." For thousands of years, people have also relied on groundwater to serve their every need. Groundwater is invaluable for many uses, from irrigation to drinking-water supply. But, you can't see groundwater, so how do water scientists know where it is in order to be able to drill wells and pump it out for use?
• Water Science School HOME • Groundwater topics •
How Do Hydrologists Locate Groundwater?
Using scientific methods to locate water
To locate groundwater accurately and to determine the depth, quantity, and quality of the water, several techniques must be used, and a target area must be thoroughly tested and studied to identify hydrologic and geologic features important to the planning and management of the resource. The landscape may offer clues to the hydrologist about the occurrence of shallow groundwater. Conditions for large quantities of shallow groundwater are more favorable under valleys than under hills. In some regions--in parts of the arid Southwest, for example--the presence of "water-loving" plants, such as cottonwoods or willows, indicates groundwater at shallow to moderate depth. Areas where water is at the surface as springs, seeps, swamps, or lakes reflect the presence of groundwater, although not necessarily in large quantities or of usable quality.
It is difficult to visualize water underground. Some people believe that ground water collects in underground lakes or flows in underground rivers. In fact, ground water is simply the subsurface water that fully saturates pores or cracks in soils and rocks. Groundwater is replenished by precipitation and, depending on the local climate and geology, is unevenly distributed in both quantity and quality. When rain falls or snow melts, some of the water evaporates, some is transpired by plants, some flows overland and collects in streams, and some infiltrates into the pores or cracks of the soil and rocks. The first water that enters the soil replaces water that has been evaporated or used by plants during a preceding dry period. Between the land surface and the aquifer water is a zone that hydrologists call the unsaturated zone. In this unsaturated zone, there usually is at least a little water, mostly in smaller openings of the soil and rock; the larger openings usually contain air instead of water. After a significant rain, the zone may be almost saturated; after a long dry spell, it may be almost dry. Some water is held in the unsaturated zone by adhesion and cohesion, and it will not flow toward or enter a well. Similar forces hold enough water in a wet towel to make it feel damp after it has stopped dripping.
Locating groundwater
Groundwater is simply the subsurface water that fully saturates pores or cracks in soils and rocks. Aquifers are replenished by the seepage of precipitation that falls on the land, although they can be artificially replenished by people, also. There are many geologic, meteorologic, topographic, and human factors that determine the extent and rate to which aquifers are refilled with water.
The landscape offers helpful clues. Shallow ground water is more likely to occur in larger quantities under valleys than under hills, because ground water obeys the law of gravity and flows downward just as surface water does. In arid regions the presence of "water-loving" plants is an indication of ground water at shallow depth. Any area where water shows up at the surface, in springs, seeps, swamps, or lakes, must have some ground water, though not necessarily in large quantity or of usable quality.
Rocks are the most valuable clues of all consolidated formations such as sandstone, limestone, or granite as well as for loose, unconsolidated sediments such as gravel or sand. An "'aquifer" is any body of rock that contains a usable supply of water. A good aquifer must be both porous enough to hold water and permeable enough to allow the continuous recharge of water to a well.
Gravel, sand, sandstone, and limestone are among the best aquifers, but they form only a fraction of the rocks in the Earth's crust. Most rocks are fine grained or otherwise '"tight" and store or carry little water.
As a first step in locating ground water, the hydrologist prepares a geologic map showing where the different kinds of rock come to the land surface. Some of the rocks may be so cracked and broken that they provide good openings to carry water underground. The rocks may be so folded and displaced, however, that it is difficult to trace their location underground.
Next, the hydrologist gathers information on the wells in the area—their locations, the depth to water, the amount of water pumped, and the kinds of rock they penetrate. Because the water-seeker cannot always afford to drill a test hole to obtain information, records of wells already drilled are of great value.
If there are no wells in the area, or not enough information is available on existing ones, the hydrologist may contract with a well driller to put down some test holes. At these holes a pumping or aquifer test will be conducted. These tests indicate the water-bearing properties of the aquifer tapped by the well. From the tests the hydrologist can determine the amount of water moving through the aquifer, the volume of water that can enter the well, and the effect of pumping on the water level of other wells in the area.
For man's use of water, quality is just as important as quantity. The hydrologist will take samples of water from different wells and have them chemically analyzed.
The hydrologist's report and geologic map will show where water can be found, its chemical composition, and in a general way, how much is available. This is the scientific approach used by the U.S. Geological Survey, State resource agencies, and consulting engineers in making their ground-water studies. Information about local ground-water conditions may be found in the offices that the U.S. Geological Survey's Water Resources Division maintains in all 50 States.
Sources/Usage: Some content may have restrictions. Visit Media to see details.Do you think you know about groundwater?
Take our Groundwater true/false quiz, part of our Activity Center.Sources and more information:
- Appraising the Nation's Ground-Water Resources, USGS General Information publication
Quiz icon made by mynamepong from www.flaticon.com
Want to know more about how hydrologists locate groundwater? Follow me to the Geophysics for USGS Groundwater/Surface Water Interaction Studies website!
- Science
Below are other science topics associated with groundwater.
Groundwater Information by Topic
Groundwater is one of our most valuable resources—even though you probably never see it or even realize it is there. There is water somewhere beneath your feet no matter where on Earth you live. Groundwater starts as precipitation, just as surface water does, and once water penetrates the ground, it continues moving, sometimes quickly and sometimes very slowly. Eventually groundwater emerges back...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.Groundwater Quality
Even though the ground is an excellent mechanism for filtering out particulate matter, such as leaves, soil, and bugs, dissolved chemicals and gases can still occur in large enough concentrations in groundwater to cause problems.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 groundwater.
A primer on ground water
Most of us don't have to look for water. We grew up either in big cities where there was a public water supply, or in small towns or on farms where the water came from wells. But there are some people to whom finding a new supply of water is vitally important.AuthorsHelene L. Baldwin, C. L. McGuinnessGround water and the rural homeowner
As the salesmen sang in the musical The Music Man, "You gotta know the territory." This saying is also true when planning to buy or build a house. Learn as much as possible about the land, the water supply, and the septic system of the house before buying or building. Do not just look at the construction aspects or the beauty of the home and surroundings. Be sure to consider the environmental condAuthorsRoger M. Waller