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Groundwater Basics Active

How important is groundwater, where's the information, active groundwater level network, well information from nearly 20,000 wells across the u.s..

  • Publications

Groundwater is the largest source of fresh water on Earth - it's kind of a big deal. The USGS monitors, tests, and studies groundwater resources to assure one of our Nation's most precious resources remains viable for future generations.

In simplest terms groundwater is what its name implies: water in the ground that fully saturates pores or cracks in soils and rocks. Water underlies the Earth's surface almost everywhere – beneath oceans, hills, valleys, mountains, lakes, and deserts. It is not always easy to get to or clean enough for use without treatment, but it exists essentially everywhere if you dig deep enough. Groundwater may occur close to the surface or it may lie many hundreds of feet below. And not all groundwater is the same age... water at very shallow depths could be just a few hours old, whereas water at great depth may have been there for several thousands years.

Most of the groundwater we extract is stored in and moves slowly through permeable rocks called  aquifers . An aquifer may be a layer of gravel or sand, a layer of sandstone or limestone, or a buried rubbly old lava flow - as long as material is saturated enough that it can yield significant quantities of water for extraction. Water is a solvent and dissolves minerals from the rocks with which it comes in contact, so groundwater may contain dissolved minerals and gases that give it a tangy taste that is familiar to many people. The most common dissolved minerals found in groundwater are sodium, calcium, magnesium, potassium, chloride, bicarbonate, and sulfate.

Diagram showing groundwater as saturated zones underground.


Generally, the quality of water found in groundwater aquifers is acceptable for most common uses like drinking or irrigation. Groundwater is less susceptible to pollution than surface water because as water enters the ground, the soil and rocks naturally filter much of the water as it passes through the ground. However, the quality of groundwater continues to change as people modify landscapes and release pollutants into the environment. The growth of industry, technology, population, and water-use demand has increased the stress on both our land and water resources. Municipal and industrial wastes and chemical fertilizers, herbicides, and pesticides have infiltrated into the soil in certain areas, percolated into local and regional aquifers, and degraded groundwater quality in many parts of the US. Other pollution problems include sewer leakage, faulty septic-tank operation, and landfill leachates. In some areas, intensive pumping of groundwater has caused groundwater tables to drop, salt water to intrude into freshwater aquifers, and land to subside (sink).

For data and information on principal aquifers in the United States:

  • The Ground Water Atlas of the United States
  • Map of the Principal Aquifers of the United States


  • Water Science School - Groundwater
  • Groundwater Use in the U.S.
  • Groundwater Watch
  • Groundwater for the Nation


  • Ground Water and Drinking Water  (U.S. Environmental Protection Agency)
  • Wellowner.org  (National Groundwater Association)

Use the links below to access web pages on examples of USGS groundwater research.

photo of man sitting on cooler working with plastic encased plastic tubing

305b Groundwater Quality Monitoring in New York

Below are data or web applications associated with this project.

USGS Groundwater Data for the Nation

Data from wells, springs, test holes, tunnels, drains, and excavations across the U.S.; well location data includes information such as latitude and longitude, well depth, and aquifer. Groundwater level data are collected and stored as either discrete field-water-level measurements or as continuous time-series data from automated recorders.

The USGS produces many types of multimedia products. Use the links below to browse our offerings of photographs, videos, and other files about groundwater.

presentation on ground water

Hazards to California's Delta Water System

This short video is one of a series of four total shorts highlighting USGS water science in California's Delta region. Earthquakes, land subsidence and flooding pose significant threats to California’s fresh water. Aqueducts, pipes and sewer lines can break and levees can breach.

presentation on ground water

Measuring Water Levels in a Flowing Well

This video demonstrates how to measure low pressure hydraulic head in a flowing well.


Groundwater 101

In this episode we explore how vital groundwater is as a natural resource and discuss what impact a changing climate and human consumption has on groundwater supplies. Join us, as we sit down with USGS Groundwater Specialist Marshall Gannett to get a primer on the role groundwater plays in our daily lives, today on the Oregon Science Podcast.

The Water Beneath Our Feet: New Study on California's Central Valley Groundwater Level Decline

SGS hydrologist Dr. Claudia Faunt discusses her new study about Calfornia's vast central valley groundwater system and the new study findings.

Here are great basic examples of USGS publications that talk about groundwater.

Ground water and the rural homeowner

What is ground water.

Below are software products associated with groundwater.

Software - MODFLOW

MODFLOW is the USGS's modular hydrologic model.  MODFLOW is considered an international standard for simulating and predicting groundwater conditions and groundwater/surface-water interactions.

Below are frequently asked questions associated with USGS groundwater research.

Aquifers: Map of the Principal Aquifers of the United States

What is the Ground Water Atlas of 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.S. Virgin Islands. Learn more: Principal Aquifers...

Water well windmill

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 who do not get their water delivered to them from...

a graph of Groundwater flow patterns and the freshwater-saltwater transition zone in an idealized coastal aquifer

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 water fills a sponge. If groundwater flows...

Glass of water

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 minerals and chemicals that are too small to see. But...


  1. PPT

    presentation on ground water

  2. PPT

    presentation on ground water

  3. The Importance Of Groundwater

    presentation on ground water

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    presentation on ground water

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    presentation on ground water

  6. How to Recharge Groundwater Explain Animation / What is Groundwater Recharge /Groundwater Harvesting

    presentation on ground water


  1. Water education: groundwater movement introduction

  2. An Introduction to Groundwater 1: What is Groundwater?

  3. What is Groundwater?

  4. Groundwater

  5. Groundwater, Seepage and Permeability Part 2

  6. Mod-01 Lec-01 Introduction : Ground Water (GW) Utilization and Historical Background


  1. Groundwater Basics

    It is difficult to visualize water underground. Groundwater 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 to nearby lakes, rivers, and wetlands.