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 groundwater can contain many different elements that are NOT filtered out by the ground and that we don't want in our drinking water. Some are naturally-occurring (like hydrogen sulfide) and some are human-made substances. Groundwater can contain petroleum, organic compounds, or other chemicals introduced by human activities.

Contaminated groundwater can occur if the well is located near land that is used for farming where certain kinds of chemicals are applied to crops, or near a gas station that has a leaking storage tank. Leakage from septic tanks and/or waste-disposal sites can also contaminate groundwater. A septic tank can introduce bacteria to the water. Pesticides and fertilizers that seep into farmed soil can eventually end up in water drawn from a well. Or, a well might have been placed in land that was once used for something like a garbage or chemical dump site. In any case, it is wise to have your well water tested for contaminants.

Learn more: Quality of Ground Water

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Why is our porcelain sink stained brown?

The brown stain is from a large amount of iron in your water. It is closely related to simple rust that you see on metal, which is iron oxide. Your water probably comes from groundwater that filtered through rocks containing iron-rich minerals on its way to the well.

Why does my drinking water look cloudy sometimes?

Once in a while you get a glass of water that looks cloudy; maybe milky is a better term. After a few seconds, it miraculously clears up! The cloudiness is due to tiny air bubbles in the water. Like any bubbles, the air rises to the top of the water and goes into the air, clearing up the water. The water in the pipes coming into your house might...

Where can I find information about my local drinking water supply?

The best way to learn about your local drinking water quality is to read the annual drinking water quality report/consumer confidence report that water suppliers now send out by July 1 of each year. The reports are often sent out with water bills, but they may be sent separately. The reports tell where drinking water comes from, what contaminants...

What can cause our water to have an earthy odor or to smell like rotten eggs?

Naturally-occurring organic compounds are created when plant material decays in lakes and reservoirs. Those organic compounds frequently cause musty, earthy odors, especially toward the end of summer. The odors can be objectionable, but generally are not harmful to health. However, odors can be caused by other constituents as well, so you might...

What can be causing our drinking water to have a reddish color?

Your water might be affected by iron, which is a commonly-occurring constituent of drinking water. Iron tends to add a rusty, reddish-brown (or sometimes yellow) color to water. If the color is more black than red, your water might contain a combination of iron and manganese. Both of these metals can cause staining of plumbing fixtures or laundry...

Do you have information about water hardness in the United States?

View a national map of hardness in surface water on the USGS water hardness website. Hardness data (reflecting mostly calcium, plus a little magnesium) for individual drinking-water suppliers is at the EPA Office of Ground Water and Drinking Water website. It is important to note that the U.S. Environmental Protection Agency (EPA) has not set a...

Where can I get my well water tested?

Contact your county or state health department or check with your State Certification Officer for a list of state certified laboratories in your area that do water testing. The cost will vary, depending on the laboratory and the test(s), but people usually consider the cost to be reasonable.

How frequently are volatile organic compounds (VOCs) detected in groundwater?

Volatile organic compounds (VOCs), which are widely used in the manufacture of many products including refrigerants, plastics, adhesives, paints, and petroleum products, have been detected in about one-third of the wells sampled by the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS). Chloroform and other...
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Date published: December 7, 2017

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

The U.S. Geological Survey is near the midpoint of a complex undertaking to survey the quality of the nation’s largest drinking-water resource.

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

Date published: December 6, 2017

Scientists Home in on Causes of High Radium Levels in Key Midwestern Aquifer

Oxygen levels, dissolved minerals among factors responsible for high concentrations of radium in untreated water from aquifer that underlies six states

Date published: October 18, 2017

Study Estimates about 2.1 Million People using Wells High in Arsenic

Most Arsenic Presumed to be From Naturally Occurring Sources

Date published: May 11, 2017

High Levels of Radon Found in Some Wells Across Pennsylvania

A new U.S. Geological Survey study has discovered high levels of radon in wells across certain areas of Pennsylvania.

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: March 6, 2017

USGS Finds Elevated Levels of Arsenic, Radon, Methane in Some Private Wells in Lycoming County, Pennsylvania

Tests of 75 private drinking water wells in Lycoming County, in north-central Pennsylvania, found water from most of the sampled wells contained concentrations of radon that exceeded a proposed, nonbinding health standard for drinking water. Smaller percentages of the wells contained concentrations of arsenic or methane that exceed existing drinking water standards.

Date published: January 19, 2017

Groundwater Quality in Eastern U.S.

A regional assessment of untreated groundwater in the combined Valley and Ridge and Piedmont and Blue Ridge aquifers in the eastern United States is now available from the U.S. Geological Survey.

Date published: July 13, 2016

New Study Shows High Potential for Groundwater to be Corrosive in Half of U.S. States

An analysis of more than 20,000 wells nationwide shows 25 states have groundwater that has either high or very high potential to be corrosive...

Filter Total Items: 15
Sampling at a pumping station
December 7, 2017

Groundwater Sampling

Collecting water samples from pumping station

April 27, 2017

Potential Corrosivity of Untreated Groundwater in the United States

  • Corrosive groundwater, if untreated, can dissolve lead and other metals from pipes.
  • National maps have been prepared to identify the occurrence of potentially corrosive groundwater in the U.S.
  • These findings have the greatest implication for the 44 million people dependent on domestic wells for drinking water.
Photo of a young girl drinking water, which likely originated from groundwater sources. 
January 17, 2017

A young girl drinks water, which likely originated from groundwater

A young girl drinks water, which likely originated from groundwater sources. 

The USGS is near the midpoint of a complex undertaking to survey the quality of the nation’s largest drinking-water resource. From 2012 – 2023, the USGS is assessing groundwater throughout the country through extensive sampling. The latest results from five regional aquifers are now

...
Drinking water from tap
December 31, 2016

Drinking water from tap

The quality of the water we drink can potentially impact our health. The USGS has several programs and cooperative projects that characterize the quality of selected rivers and aquifers used as sources of drinking water to community water systems in the United States.

Attribution: Water Resources
September 1, 2016

Drought, Drinking Water and Natural Environments

This short video is one of a series of four total shorts highlighting USGS water science in California's Delta region. The Sacramento-San Joaquin Delta is the hub of the state's water system. Water quality touches on all aspects of life. Teams of U.S. Geological Survey scientists along with their partners monitor water quality and identify sources of pollution and

...
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
...
February 10, 2010

Why Some Public-Supply Wells are More Vulnerable to Contamination Than Others

This video discusses how scientists have tracked what, when, and how contaminants may reach public-supply wells in four aquifers in California, Connecticut, Nebraska, and Florida.

USGS
May 5, 2009

New NAWQA Study Documents Contamination in Domestic Wells

USGS Hydrologist Jill Frankforter discusses recent findings from a new USGS study on contamination in water drawn from domestic wells. She also discusses how the findings for Nebraska compared to the nation.

USGS
November 18, 2008

Why does my drinking water look milky or cloudy sometimes?

Listen to hear the answer.

USGS
September 30, 2008

What is E. coli and what should I do if it is in my drinking water?

Listen to hear the answer.

Collecting groundwater samples from a municipal well as part of the NAWQA Principal Aquifer Study in Nebraska

Collecting groundwater samples from a municipal well, Nebraska

Collecting groundwater samples from a municipal well as part of the NAWQA Principal Aquifer Study in Nebraska.