What is groundwater?Groundwater is used for drinking water by more than 50% of the people in the United States, including almost everyone who lives in rural areas.
Groundwater lies almost everywhere below the earth’s surface. More than two million cubic miles of fresh water is stored in the earth, and half of that is within a half mile of the surface. Fifty percent of the U.S. population depends on groundwater daily for drinking. In addition, groundwater is one of our most important sources of irrigation.
When rain falls to the ground, the water does not stop moving. Some of it flows along the surface in streams or lakes, some of it is used by plants, some evaporates and returns to the atmosphere, and some sinks into the ground. Imagine pouring a glass of water onto a pile of sand. Where does the water go? The water moves into the spaces between the particles of sand.
Groundwater is water that is found underground in cracks and spaces in soil, sand and rocks. The area where water fills these spaces is called the saturated zone. The top of this zone is called the water table…just remember the top of the water is the table. The water table may be only a foot below the ground’s surface or it may be hundreds of feet down.
Groundwater can be found almost everywhere. The water table may be deep or shallow; and may rise or fall depending on many factors. Heavy rains or melting snow may cause the water table to rise, or an extended period of dry weather may cause the water table to fall.
Groundwater is stored in–and moves slowly through–layers of soil, sand and rocks called aquifers. The speed at which groundwater flows depends on the size of the spaces in the soil or rock and how well the spaces are connected.
Aquifers typically consist of gravel, sand, sandstone, or fractured rock, like limestone. These materials are permeable because they have large connected spaces that allow water to flow through.
Water in aquifers is brought to the surface naturally through a spring or can be discharged into lakes and streams. This water can also be extracted through a well drilled into the aquifer. A well is a pipe in the ground that fills with groundwater. This water then can be brought to the surface by a pump. Shallow wells may go dry if the water table falls below the bottom of the well. Some wells, called artesian wells, do not need a pump because of natural pressures that force the water up and out of the well.
Groundwater supplies are replenished, or recharged, by rain and snow melt. In some areas of the world, people face serious water shortages because groundwater is used faster than it is naturally replenished. In other areas groundwater is polluted by human activities.
In areas where material above the aquifer is permeable, pollutants can sink into the groundwater. Groundwater can be polluted by landfills, septic tanks, leaky underground gas tanks, and from overuse of fertilizers and pesticides. If groundwater becomes polluted, it will no longer be safe to drink.
Groundwater is used for drinking water by more than 50% of the people in the United States, including almost everyone who lives in rural areas. The largest use for groundwater is to irrigate crops.
It is important for all of us to learn to protect our groundwater.
Why do we depend on groundwater?According to United States Geological Survey (USGS) figures, groundwater provides an estimated:
- 22% of all freshwater withdrawals
- 37% of agricultural use (mostly for irrigation)
- 37% of the public water supply withdrawals
- 51% of all drinking water for the total population
- 99% of drinking water for the rural population
How do we protect our groundwater?Unfortunately, contaminated groundwater is very difficult and expensive to clean up. Solutions can be found after groundwater has been contaminated but this isn’t always easy. The best thing to do is adopt pollution prevention and conservation practices in order to protect important groundwater supplies from being contaminated in the first place.
Pollution PreventionMany steps are being taken to keep pollutants from reaching groundwater supplies. Manufacturers are using fewer toxic raw materials. Consumers have switched to phosphate-free detergents and other less polluting household products. Pollution control measures such as the Clean Water Act have also been a big part of the protection of drinking water supplies.
Groundwater ConservationGroundwater is available in limited quantities. Since groundwater is an important resource for so many people, it is important to protect it. Protecting the quantity of groundwater is easy. By simply reducing the amount of water that we use, our water supply will last longer.
What are groundwater contamination concerns?Fifty percent of the United States population depends daily on groundwater for their drinking water. Groundwater is also one of our most important sources of irrigation water. Unfortunately, groundwater is susceptible to pollutants. Groundwater is generally a safe source of drinking water, however, there are concerns that contamination may increase as toxins dumped on the ground in the past make their way into groundwater supplies.
Pollutants LeachPollutants that contaminate groundwater may be some of the same pollutants that contaminate surface water. Compounds from the surface can move through the soil and end up in the groundwater. For example, pesticides and fertilizers can find their way into groundwater supplies over time. Road salt, toxic substances from mining sites, and used motor oil also may seep into groundwater. In addition, it is possible for untreated waste from septic tanks and toxic chemicals from underground storage tanks to contaminate groundwater.
Dangers of Contaminated GroundwaterDrinking contaminated groundwater can have serious health effects. Diseases such as hepatitis and dysentery may be caused by contamination from septic tank waste. Poisoning may be caused by toxins that have leached into well water supplies. And it is important not to forget that wildlife, too, can be harmed by contaminated groundwater.
What are sources of groundwater contamination?Groundwater contamination occurs when man-made products such as gasoline, oil, road salts and chemicals get into the groundwater and cause it to become unsafe and unfit for human use. Some of the major sources of these products, called contaminants, are storage tanks, septic systems, hazardous waste sites, landfills, and the widespread use of road salts and chemicals.Storage tanks may contain gasoline, oil, chemicals, or other types of liquids and they can either be above or below ground. There are estimated to be over 10 million storage tanks that are buried in the United States and over time the tanks can corrode and crack and leaks can develop. If the contaminants leak out and get into the groundwater, serious contamination can occur.
Septic systems can be another serious contamination source. Septic systems are for homes, offices or other buildings that are not connected to a city sewer system. Septic systems are designed to slowly drain away human waste underground at a slow, harmless rate. An improperly designed, located, constructed, or maintained septic system can leak bacteria, viruses, household chemicals, and other contaminants into the groundwater causing serious problems.
In the United States today, there are thought to be over 20,000 known abandoned and uncontrolled hazardous waste sites and the numbers grow every year. Hazardous waste sites can lead to groundwater contamination if there are barrels or other containers laying around that are full of hazardous materials. If there is a leak, these contaminants can eventually make their way down through the soil and into the groundwater.
Landfills are another major source of contamination. Landfills are the places that our garbage is taken to be buried. Landfills are supposed to have a protective bottom layer to prevent contaminants from getting into the water. However, if there is no layer or it is cracked, contaminants from the landfill (car battery acid, paint, household cleaners, etc.) can make their way down into the groundwater.
Finally, the widespread use of road salts and chemicals can also lead to groundwater contamination. Road salts are used in the wintertime to put melt ice on roads to keep cars from sliding around. When the ice melts, the salt gets washed off the roads and eventually ends up in the water. Chemicals include products used on lawns and farm fields to kill weeds and insects and to fertilize the plants. When the rain comes, these chemicals get washed into the ground and eventually into the water.
We have to remember that since groundwater is part of the hydrologic cycle, what can contaminate other parts of the cycle, such as the air or surface water, can eventually get into the groundwater.
What are some tips to protecting and conserving groundwater?
- Dispose of chemicals properly.
- Take used motor oil to a recycling center.
- Limit the amount of fertilizer used on plants.
- Take short showers.
- Shut water off while brushing teeth.
- Run full loads of dishes and laundry.
- Check for leaky faucets and have them fixed.
- Water plants only when necessary.
- Keep a pitcher of drinking water in the refrigerator.
- Get involved in water education.