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.
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Groundwater Quality
Credit: Howard Perlman, USGS
Just because you have a well that yields plenty of water doesn't mean you can go ahead and just take a drink. Because water is such an excellent solvent it can contain lots of dissolved chemicals. And since groundwater moves through rocks and subsurface soil, it has a lot of opportunity to dissolve substances as it moves. For that reason, groundwater will often have more dissolved substances than surface water will.
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. Underground water can get contaminated from industrial, domestic, and agricultural chemicals from the surface. This includes chemicals such as pesticides and herbicides that many homeowners apply to their lawns.
Contamination of groundwater by road salt is of major concern in northern areas of the United States. Salt is spread on roads to melt ice, and, with salt being so soluble in water, excess sodium and chloride is easily transported into the subsurface groundwater. The most common water-quality problem in rural water supplies is bacterial contamination from septic tanks, which are often used in rural areas that don't have a sewage-treatment system. Effluent (overflow and leakage) from a septic tank can percolate (seep) down to the water table and maybe into a homeowner's own well. Just as with urban water supplies, chlorination may be necessary to kill the dangerous bacteria.
The U.S. Geological Survey (USGS) is involved in monitoring the Nation's groundwater supplies. A national network of observation wells exists to measure regularly the water levels in wells and to investigate water quality.
Contaminants can be natural or human-induced
View a long list of chemicals and contaminants that can be found in groundwater.
Naturally occurring contaminants are present in the rocks and sediments. As groundwater flows through sediments, metals such as iron and manganese are dissolved and may later be found in high concentrations in the water. Industrial discharges, urban activities, agriculture, groundwater pumpage, and disposal of waste all can affect groundwater quality. Contaminants from leaking fuel tanks or fuel or toxic chemical spills may enter the groundwater and contaminate the aquifer. Pesticides and fertilizers applied to lawns and crops can accumulate and migrate to the water table.
Credit: USGS
Groundwater can contain hydrogen sulfide or other naturally occurring chemicals. Groundwater also may contain petroleum, organic compounds, or other chemicals introduced by humans' 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 also can contaminate groundwater. A septic tank can introduce bacteria to the water, and 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 contaminates.
The physical properties of an aquifer, such as thickness, rock or sediment type, and location, play a large part in determining whether contaminants from the land surface will reach the groundwater. The risk of contamination is greater for unconfined (water-table) aquifers than for confined aquifers because they usually are nearer to land surface and lack an overlying confining layer to impede the movement of contaminants. Because groundwater moves slowly in the subsurface and many contaminants sorb to the sediments, restoration of a contaminated aquifer is difficult and may require years, decades, centuries, or even millennia.
Many Americans drink groundwater from their own wells
If you drive on a rural highway almost anywhere in the Nation you might see some small "doghouse-looking" enclosures or some metal pipes and tubing in the side yard of many homes and trailer parks. These are small wells that supply domestic water to individual and small groups of families.
If you ask them if the possible contamination of groundwater is of interest to them, they would have to say "yes". This is the case with tens of millions of people across the country. The map below shows the percentage of each State's population that relies on their own well water for home use. Percentages range from 1 percent in Puerto Rico to 44 percent in Maine, with the National average being 14 percent. You can view this and other maps and the corresponding data from the USGS publication "Estimated Use of Water in the United States, 2015".
Some information on this page is from Ground Water and the Rural Homeowner, Pamphlet, U.S. Geological Survey, 1982, by Roger M. Waller
Want to learn more about groundwater quality? Follow me to the Groundwater Quality Research website!
Below are other science topics associated with groundwater quality.
Groundwater Information by Topic
Aquifers and Groundwater
Water Quality Information by Topic
Groundwater True/False Quiz
Water, the Universal Solvent
Domestic Water Use
Contamination of Groundwater
Groundwater Wells
Below are multimedia resources related to groundwater quality.
- Overview
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.
• Water Science School HOME • Groundwater topics • Water Quality topics •
Groundwater Quality
Sources/Usage: Some content may have restrictions. Visit Media to see details.Groundwater usually looks crystal clear, but before drinking it, care must be taken to make sure it doesn't contain dissolved chemicals that could be harmful.
Credit: Howard Perlman, USGSJust because you have a well that yields plenty of water doesn't mean you can go ahead and just take a drink. Because water is such an excellent solvent it can contain lots of dissolved chemicals. And since groundwater moves through rocks and subsurface soil, it has a lot of opportunity to dissolve substances as it moves. For that reason, groundwater will often have more dissolved substances than surface water will.
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. Underground water can get contaminated from industrial, domestic, and agricultural chemicals from the surface. This includes chemicals such as pesticides and herbicides that many homeowners apply to their lawns.
Contamination of groundwater by road salt is of major concern in northern areas of the United States. Salt is spread on roads to melt ice, and, with salt being so soluble in water, excess sodium and chloride is easily transported into the subsurface groundwater. The most common water-quality problem in rural water supplies is bacterial contamination from septic tanks, which are often used in rural areas that don't have a sewage-treatment system. Effluent (overflow and leakage) from a septic tank can percolate (seep) down to the water table and maybe into a homeowner's own well. Just as with urban water supplies, chlorination may be necessary to kill the dangerous bacteria.
Sources/Usage: Public Domain.The U.S. Geological Survey (USGS) is involved in monitoring the Nation's groundwater supplies. A national network of observation wells exists to measure regularly the water levels in wells and to investigate water quality.
Contaminants can be natural or human-induced
View a long list of chemicals and contaminants that can be found in groundwater.
Naturally occurring contaminants are present in the rocks and sediments. As groundwater flows through sediments, metals such as iron and manganese are dissolved and may later be found in high concentrations in the water. Industrial discharges, urban activities, agriculture, groundwater pumpage, and disposal of waste all can affect groundwater quality. Contaminants from leaking fuel tanks or fuel or toxic chemical spills may enter the groundwater and contaminate the aquifer. Pesticides and fertilizers applied to lawns and crops can accumulate and migrate to the water table.
Sources/Usage: Public Domain. Visit Media to see details.One USGS model, based on nationwide data, was developed to estimate the risk of nitrate contamination to shallow ground water across the United States. The model integrates nitrogen inputs and aquifer vulnerability by use of Geographic Information System (GIS) technology. Nitrogen inputs include commercial fertilizer and manure application rates, atmospheric contributions, and population densities (the latter representing residential and urban nitrogen sources, such as septic systems, fertilizers, and domestic animal waste). Aquifer vulnerability is represented by soil-drainage characteristics—the ease with which water and chemicals can seep to ground water—and the extent to which woodlands are interspersed with cropland.
Credit: USGSGroundwater can contain hydrogen sulfide or other naturally occurring chemicals. Groundwater also may contain petroleum, organic compounds, or other chemicals introduced by humans' 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 also can contaminate groundwater. A septic tank can introduce bacteria to the water, and 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 contaminates.
The physical properties of an aquifer, such as thickness, rock or sediment type, and location, play a large part in determining whether contaminants from the land surface will reach the groundwater. The risk of contamination is greater for unconfined (water-table) aquifers than for confined aquifers because they usually are nearer to land surface and lack an overlying confining layer to impede the movement of contaminants. Because groundwater moves slowly in the subsurface and many contaminants sorb to the sediments, restoration of a contaminated aquifer is difficult and may require years, decades, centuries, or even millennia.
Many Americans drink groundwater from their own wells
If you drive on a rural highway almost anywhere in the Nation you might see some small "doghouse-looking" enclosures or some metal pipes and tubing in the side yard of many homes and trailer parks. These are small wells that supply domestic water to individual and small groups of families.
If you ask them if the possible contamination of groundwater is of interest to them, they would have to say "yes". This is the case with tens of millions of people across the country. The map below shows the percentage of each State's population that relies on their own well water for home use. Percentages range from 1 percent in Puerto Rico to 44 percent in Maine, with the National average being 14 percent. You can view this and other maps and the corresponding data from the USGS publication "Estimated Use of Water in the United States, 2015".
Sources/Usage: Public Domain. Visit Media to see details.Significant percentages of each state's population supply their own home water via wells. Some information on this page is from Ground Water and the Rural Homeowner, Pamphlet, U.S. Geological Survey, 1982, by Roger M. Waller
Sources/Usage: Public Domain.Want to learn more about groundwater quality? Follow me to the Groundwater Quality Research website!
- Science
Below are other science topics associated with groundwater quality.
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...Aquifers and Groundwater
A huge amount of water exists in the ground below your feet, and people all over the world make great use of it. But it is only found in usable quantities in certain places underground — aquifers. Read on to understand the concepts of aquifers and how water exists in the ground.Water Quality Information by Topic
What is in that water that you just drank? Is it just hydrogen and oxygen atoms? Is it safe for drinking? All water is of a certain "quality" (and you can't tell by just looking), but what does "water quality" really mean? Water full of dirt and grime might work fine for a tomato plant but would you want to drink it? Water quality can be thought of as a measure of the suitability of water for a...Groundwater True/False Quiz
How much do you know about the water below your feet? Take our Groundwater True/False Quiz and find out.Water, the Universal Solvent
We need to take the statement "Water is the universal solvent" with a grain of salt (pun intended). Of course it cannot dissolve everything, but it does dissolve more substances than any other liquid, so the term fits pretty well. Water's solvent properties affect all life on Earth, so water is universally important to all of us.Domestic Water Use
Domestic water use is water used for indoor and outdoor household purposes— all the things you do at home: drinking, preparing food, bathing, washing clothes and dishes, brushing your teeth, watering the garden, and even washing the dog. At the U.S. Geological Survey (USGS), domestic water use refers to the amount of water that is "self-supplied", or water withdrawn directly by users, such as from...Contamination of Groundwater
Groundwater will normally look clear and clean because the ground naturally filters out particulate matter. But did you know that natural and human-induced chemicals can be found in groundwater even if appears to be clean? Below is a list of some contaminants that can occur in groundwater.Groundwater Wells
Wells are extremely important to all societies. In many places wells provide a reliable and ample supply of water for home uses, irrigation, and industries. Where surface water is scarce, such as in deserts, people couldn't survive and thrive without groundwater, and people use wells to get at underground water. - Data
- Multimedia
Below are multimedia resources related to groundwater quality.
- Publications