What is the difference between a confined and an unconfined (water-table) aquifer?

A confined aquifer is an aquifer below the land surface that is saturated with water. Layers of impermeable material are both above and below the aquifer, causing it to be under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer.

A water-table--or unconfined--aquifer is an aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall. Water-table aquifers are usually closer to the Earth's surface than confined aquifers are, and as such are impacted by drought conditions sooner than confined aquifers.

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Do you have maps of aquifers and groundwater in the United States?

This Ground Water Atlas of the United States is a series of USGS publications that describe the location, the extent, and the geologic and hydrologic characteristics of the important aquifers of the Nation. The series consists of 13 chapters that describe the regional groundwater resources that collectively cover 50 States, Puerto Rico, and the U...

How can I find the depth to the water table in a specific location?

The depth to the water table can change (rise or fall) depending on the time of year. During the late winter and spring when accumulated snow starts to melt and spring rainfall is plentiful, water on the surface infiltrates into the ground and the water table rises. When water-loving plants start to grow again in the spring and precipitation gives...

What determines if a well will go dry?

A well is said to have gone dry when water levels drop below a pump intake. This does not mean that a dry well will never have water in it again, as the water level may come back through time as recharge increases. The water level in a well depends on a number of things, such as the depth of the well, the type (confined or unconfined) of aquifer...

If the ground filters water, is groundwater always clean?

Water drawn from a well was once precipitation that fell onto Earth's surface. It seeped into the ground and, over time, occupied the porous space in some subsurface material. Big particles that are in surface streams, such as leaf chunks, will not be seen in groundwater. So, yes, big particles are filtered out by the ground, along with some...

How important is groundwater?

Groundwater, which is in aquifers below the surface of the Earth, is one of the Nation's most important natural resources. Groundwater is the source of about 37 percent of the water that county and city water departments supply to households and businesses (public supply). It provides drinking water for more than 90 percent of the rural population...

What is groundwater?

Groundwater is water that exists underground in saturated zones beneath the land surface. The upper surface of the saturated zone is called the water table. Contrary to popular belief, groundwater does not form underground rivers. It fills the pores and fractures in underground materials such as sand, gravel, and other rock, much the same way that...
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Date published: April 12, 2018

USGS Releases New Web-Based Groundwater Model Visualization Tool

A new U.S. Geological Survey groundwater model visualization tool is now available to help users visualize the inputs and outputs of complex groundwater models across the country.

Date published: January 24, 2018

Alaska Earthquake Rattles Florida’s Groundwater Plumbing

At 12:32 am Alaska time on January 23, 2018, a magnitude 7.9 earthquake shook Alaska residents out of their beds and set off fears of a tsunami all down the West Coast. Fortunately, the tsunami was only a few inches in height, but within an hour of the earthquake in Alaska, waves of a different sort were hitting far away in Florida. 

Date published: December 7, 2017

The Quality of the Nation’s Groundwater: Progress on a National Survey

The U.S. Geological Survey makes progress on a complex undertaking to survey the quality of the nation’s largest drinking-water sources.

New reports assess the quality of drinking-water supplies in three Western and Southwestern regional aquifers, adding to 15 previously assessed across the nation.

Current website: https://www.usgs.gov/news/quality-nation-s-groundwater-progress-a-national-survey

Date published: March 9, 2017

How Well Do You Know Groundwater

Groundwater, which flows out of sight through aquifers beneath our feet, is one of the Nation’s most important natural resources. In recognition of National Groundwater Awareness Week, March 5–11, 2017, here’s an opportunity to put your knowledge of this vital resource to the test!

Attribution: Water Resources
Date published: December 14, 2016

How Much Water Do We Use?

The USGS National Water-Use Science project has documented 60 years of water-use from 1950 to 2010 in an interactive map.  Choose a year and pick a category to see how much water your state uses. 

Attribution: Water Resources
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Flowing artesian well in Brunswick, Georgia, USA
October 7, 2019

Flowing artesian well in Brunswick, Georgia, USA

Groundwater in aquifers between layers of poorly permeable rock, such as clay or shale, may be confined under pressure. If such a confined aquifer is tapped by a well, water will rise above the top of the aquifer and may even flow from the well onto the

A diagram showing a cross-section of the subsurface, including the unsaturated zone.
April 27, 2016

A diagram showing a cross-section of the subsurface, including the unsaturated zone.

A diagram showing a cross-section of the subsurface, including the unsaturated zone. Credit: USGS

USGS scientist collects a groundwater-level measurement in Freeport, Texas. 
January 31, 2016

Collecting a groundwater-level measurement in Freeport, Texas

USGS hydrologist Jason Ramage collects a groundwater-level measurement using a steel tape in Freeport, Texas. 

A new interactive web application illustrates how groundwater, sediment compaction and land-elevation change are related in the Houston-Galveston region in Texas. 

USGS scientists collecting water-quality samples from shallow groundwater under Ashumet Pond
July 3, 2014

USGS Scientists Collecting Water-Quality Samples from Shallow Groundwater under Ashumet Pond

U.S. Geological Survey (USGS) scientists collecting water-quality samples from shallow groundwater under Ashumet Pond, Cape Cod, Massachusetts. The scientists collected the samples to understand importance of lake sediments in removal of cyanobacteria, viruses, and dissolved

September 22, 2011

PubTalk 9/2011 — Tracking the Nation's Groundwater Reserves

--issues facing current and future water supplies

by William Alley, USGS Office of Groundwater


  • Ground water is among the Nation's most important natural resources, providing half of our drinking water as well as being essential to agriculture and industry, and the health of ecosystems throughout the country
Real-time Groundwater Streamgage equipment set up
June 15, 2011

Real-time Groundwater Streamgage equipment set up

Real-time Groundwater Streamgage equipment set up

January 6, 2009

What is "artesian well water"?

Listen to hear the answer.

illustration of cross-sectional view of Long Island aquifer system
November 30, 2000

Long Island Sole-source aquifer system

Sole-source aquifer system - This representative cross-sectional view of the Long Island aquifer system shows that about 630 Bgal/d of water enters the flow system as recharge at the water table from rainfall and flows in the subsurface until either discharging to ponds, streams, coastal waters or pumping wells. Groundwater withdrawals remove as much as 23

Image: Artesian Well Investigations
June 30, 1957

Artesian Well Investigations

Artesian well investigations in South Dakota (circa-July 1957).

Attribution: Water Resources
illustration of setup of homeowner well

Groundwater sampling of a typical homeowner well

Groundwater sampling of a typical homeowner well: Samples at production wells are usually collected where PWS personnel collect raw water samples (can be at tap off main line, spigot, sink, hydrant, etc.)