Groundwater FAQs

Answers to Frequently Asked Questions About Groundwater

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Water Use in the United States

1. Why is water important?
2. What is most of the fresh water in the U.S. used for?
3. Which states use the most water, and for what purposes?
4. Where does irrigation water come from and how is it applied to the land?
5. How important is ground water?

Ground Water Basics

6. What is the difference between ground and surface water?
7. How does water get underground?
8. Where does artesian water come from?

Water Use at Home

9. Where does our household water come from?
10. Where does household water go after we are done with it?
11. How much water does the average person use at home per day?
12. How is water supplied to our homes?
13. How is the water I drink made safe?
14. Does a little leak in my house really waste water?

Chemical Properties

15. Why does my water smell like rotten eggs?
16. Why does it take so long to rinse the soap off my hands?
17. Why is our porcelain sink stained brown?
SOURCE: U.S. Geological Survey
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1. Why is water important?

All animals need water to survive. Both water availability and water quality are critical issues. At a basic level, pretty much everything we eat has some water in it. It takes water to either grow or make our foods. This water is either supplied by nature as precipitation or added by man during the growing/production process. You can't tell by the size or texture of a food how much water was used to actually produce the food item. For example:

FOOD# Gallons to create
a single serving
almonds12
chicken408
french fries6
hamburger1303
lettuce6
milk65
rice36
steak2607
tomatoes3
watermelon100

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2. What is most of the fresh water in the U.S. used for?

In 1990, about 339,000 million gallons per day of fresh water was withdrawn from our surface and ground water sources, such as wells, rivers, lakes, and reservoirs. Here's the breakdown by water-use category:

Irrigation40 %
Thermoelectric power39 %
Public Supply11 %
Industry6 %
Livestock1 %
Domestic1 %
Mining1 %
Commercial1 %

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3. Which states use the most water, and for what purposes?

In 1990, California alone accounted for over 10 % of all freshwater used in the United States. After California was Texas, Idaho, and Illinois, which together accounted for one-quarter of all water withdrawn in the U.S. Most of the water used in California was for crop irrigation. In fact, one-fifth of all irrigation withdrawals in the country were in California, which indicates how important agriculture is there. Florida also is a large food producer but since it gets a lot more summer rainfall than the central valley of California, there is less need to apply irrigation water.

The three most populated states, California, New York, and Texas accounted for almost one-third of all water withdrawn for public-supply uses (such as a city withdrawing water to distribute for uses around town). One state, Louisiana, acccounted for over 12 % of the nation's livestock water withdrawals - you might be surprised that most of this water was used for "fish farming"? West Virginia and Florida were the highest users of mining withdrawals, and California and Florida withdrew the most water for domestic purposes.

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4. Where does irrigation water come from and how is it applied to the land?

Both ground water and surface water are used for irrigation. In 1990, about 51,000 million gallons per day were withdrawn from the ground for irrigation, whereas about 85,500 million gallons per day was taken from surface-water sources. A small amount of reclaimed wastewater coming from sewage-treatment plants, about 660 million gallons per day was used for irrigation. The USGS keeps records on the types of irrigation systems used in the United States. One method is called flood irrigation, where water flows onto the land. Another method is called spray irrigation where water is sprayed or dripped on the crops. In 1990, about 34,500,000 acres out of the 57,400,000 total irrigated acres (about 60 %), were irrigated by the flood process. The other 40 % of land was spray irrigated. How the acres are irrigated in the major irrigation states is illustrated in the following table:

StateAcres irrigated
(thousands)
% acres
sprayed
% acres
flooded
 
Arizona1,35030%70%
Arkansas3,00010%90%
California9,50024%76%
Colorado3,55025%75%
Florida2,15047%53%
Georgia1,180100%0%
Hawaii13091%9%
Michigan367100%0%
Nebraska6,86044%56%
N. Carolina180100%0%
S. Dakota40072%28%
Texas6,22035%65%
Utah1,30035%65%
Washington1,98076%24%
Wyoming1,94011%89%

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5. How important is ground water?

Ground water, which is in aquifers below the surface of the Earth, is among the Nation's most important natural resources. Ground water is the source of about 40 % of the water used for public supply. It provides drinking water for more than 97 % of the rural population who do not have access to public water-supply systems. Even some major cities, such as San Antonio, Texas, rely solely on ground water for all their needs. Between 30 and 40 % of the water used for agriculture comes from ground water. Withdrawals of ground water are expected to rise in the coming century as the population increases and available sites for surface reservoirs become more limited.

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6. What is the difference between surface and ground water?

Surface water is water found over the land surface in streams, ponds, marshes, lakes or other fresh (not salty) sources. Ground water is water occurring in the zone of saturation in an aquifer or soil. Other than the location, one of the primary differences between surface and ground water is that ground water moves much slower than surface water. This is because ground water experiences far more friction as it moves through the pores in soil then surface water experiences as it flows over the earth's surface. Surface water is much more easily contaminanted than ground water. Filtration through the soil helps clean ground water.

 

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7. How does water get underground?

A portion of the precipitation (rain, hail, snow) that lands on the ground will enter the soil. This process is called infiltration. Because of gravity, the filling or saturation of spaces between soil particles, and the pressure of the overlying water, water may continue to move down through the soil layer. As water moves past the root zone, the movement is referred to as percolation. Layers of soil and rock that are saturated with water are called aquifers. Aquifers are able to transport water and supply water to wells, rivers, springs and marshes. A ground surface area that provides a water entry port for a confined aquifer is called a recharge area or zone.

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8. Where does artesian water come from?

Artesian water is a phrase found on many bottled water containers and other refreshment products. Artesian water comes from an artesian water source - a confined aquifer in which the water is under enough pressure that, when tapped by a well, the underground water rises above the level of the aquifer surface. In some cases, the water in the aquifer is under sufficient pressure to push the water right up and over the ground surface. Such wells are called flowing artesian wells.

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9. Where does our household water come from?

All of the water that we use in our homes comes from either a ground water source, such as a well, or from a surface water source, such a river, lake, or reservoir. In the U.S. in 1990, we used about 9,240 billion gallons of water for domestic purposes. Of that, about 44 % came from ground water sources, and about 56 % came from surface water sources.

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10. Where does household water go after we are done with it?

Water leaving our homes generally either goes into a septic tank in the back yard where it evaporates or seeps back into an aquifer, or is returned to a sewage-treatment plant through a sewer system. In 1990, about 23 % of the water coming from our homes was "consumptively used". That is, it was evaporated or transpired from yards. The rest, about 77 % was discharged to septic tanks or sewage-treatment plants, and that water was then available for further use by someone else.

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11. How much water does the average person use at home per day?

percent water consumption diagram Estimates vary, but each person uses about 75-100 gallons of water per day. Are you surprised that the largest use of household water is to flush the toilet, and after that, to take showers and baths? That is why in these days of water conservation, we are starting to see toilets and showers that use less water than before.


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12. How is water supplied to our homes?

In a modern society such as ours, much work goes into supplying our houses with water. Many years ago when everyone lived in rural areas, they would have to get their own water from rivers or from local wells. Now most people in the U.S. live in towns and cities, and the government in those areas have an organized structure called a public water-supply system to provide water to homes. In 1990, the U.S. had a population of about 253 million. About 210 million people had their water delivered from a public-supply system, and about 43 million people supplied their own water (97 % of these people use water from their own wells).

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13. How is the water I drink made safe?

Different treatment is used depending on the source of your water. Ground water taken from wells has been filtered through rocks, so it is usually quite free of particles. It can still contain chemicals and organic matter that must be taken out, though. If your water comes from a surface-water source, such as a river, some work must be done to get rid of particulate matter. In this case filters are used to screen out large particles, and at a minimum, chlorine is added to kill dangerous bacteria and microorganisms. Some systems have additional water treatment, such as adding chemicals to make matter bunch up and fall out of solution and adding chemicals to make the water less corrosive to metal.

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14. Does a little leak in my house really waste water?

It's not the little leak that wastes water ... it is the little leak that keeps on leaking that wastes water. And the fact that the leak is so little means that maybe you ignore it. So, how can a little leak turn into a big waste? Many of our toilets have a constant leak - somewhere around 22 gallons per day. This translates into about 8,000 gallons per year of wasted water, water that could be saved. Or think of a leaky water line coming into your house. If it leaks 1 gallon of water every 10 minutes that means that you are losing (and paying for) 144 gallons per day, or 52,560 gallons per year.

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15. Why does my water smell like rotten eggs?

You would know it if you had this problem! In some parts of the country, drinking water can contain the chemical hydrogen sulfide, which smells just like rotten eggs. This can occur when water comes into contact with organic matter or with some minerals, such as pyrite. The situation mostly occurs as ground water filters through organic material or rocks.

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16. Why does it take so long to rinse the soap off my hands?

hard water scale fact diagram The terms "soft water" and "hard water" are important here. Water is said to be "soft" if it has a low concentration of calcium and magnesium ions in it, and "hard" water has a higher concentration. The ions react with the soap you use to produce a scummy residue that is hard to wash off. If you use "hard" water you also will have a harder time working the soap up into a lather. "Hard" water is prevalent in some parts of the country, and sometimes "water softening" chemicals, that reduce the amount of calcium and magnesium, are added to the water.

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17. Why is our porcelain sink stained brown?

The brown stain is from too much iron in your water. It is closely related to simple rust you see on metal, which is iron oxide. Probably the source of the water you use is ground water, and the water has filtered through rocks containing iron-rich minerals on the way to the well.

 

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