Supplies, Public and Domestic Water
Water supplies are needed for public, domestic (private), commercial, agricultural, and industrial uses. Public water supplies are those supplied by a public agency in populated areas for all these purposes. Domestic supplies refer to individual homes, often in rural areas, that have their own water source and piping. About 93 percent of the U.S. population receives their water from public water systems, and 7 percent from domestic supplies.
Water Supplies Then and Now
Civilizations often developed as a result of their proximity to water. As human populations became more concentrated, human and animal waste began to degrade the quality of water supplies. The ancient Romans were the first to recognize the benefits of transporting fresh water into a densely populated area. In the first century C . E ., the first known aqueduct was constructed to carry water for more than 32 kilometers (20 miles). Since that time, water systems have become more sophisticated, and water planners have learned more about the connection between water quality and public health.
Water historically has been one of the most significant modes of transmitting disease. In many parts of the world, lack of proper sanitation facilities and clean water supplies still cause millions of people to suffer and die from waterborne illnesses annually.
In the United States, the federal Safe Drinking Water Act regulates public water supplies. Additional regulations have been added since passage of the Act in 1974. This legislation requires that all public water supplies, defined as those serving 25 or more people, or having 14 or more service connections, must routinely test their water to ensure it is safe for people to drink. Domestic water supplies are excluded from these requirements, so the owner can choose whether to conduct private testing.
Contaminants in Water
Microorganisms found in fecal matter have the potential to cause serious and immediate illnesses. Public water suppliers must regularly test for the presence of these organisms. Inorganic chemicals, volatile and synthetic organic chemicals, and radiological chemicals are monitored every 1 to 4 years because the adverse health effects they cause occur over long-time exposure to the contaminant.
Inorganic compounds can be naturally occurring, from fertilizers, or the result of metals leaching from pipes and faucets. Synthetic organic chemicals include pesticides and herbicides used for agricultural purposes. Volatile organic chemicals are found in compounds such as fuels, oils, or solvents. Radiological compounds, a byproduct of natural and human-made processes, are also monitored. Consumption of these contaminants has been shown to have negative health effects, ranging from diarrhea to various types of cancer.
Sources of Water
There are several collection sources as water falls to Earth in the form of precipitation.
Water that gathers on the surface is called surface water. Lakes, rivers, and streams are examples of fresh surface water that can be used as sources of drinking water. Dams are often constructed in a river to form an impoundment, allowing for storage of water. Approximately twothirds of the U.S. population consumes water from surface-water sources.
Water found in water-bearing sediment or rock formations beneath the ground surface is known as groundwater. Groundwater is a major drinking water source, and is obtained by a water well or cluster of wells. Almost all domestic supplies are groundwater wells. Approximately onethird of the U.S. population drinks water from groundwater sources.
Where a water-bearing formation intercepts the ground surface, usually on a hillside, a spring emerges. A spring can be captured for a water-supply source as either surface water or groundwater. If the spring water is captured inside the hillside before it emerges, it is considered groundwater. If the spring water is allowed to flow on the surface, it becomes surface water.
Although not a major source of water in the United States, rainwater can be collected and stored in a cistern or storage tank for domestic use. The surface where the rain is collected, usually a roof, must be cleaned frequently. Rainwater is most commonly used as a source of supply where other sources are scarce.
Water Treatment and Distribution
If harmful contaminants are present, the water must be treated to protect human health. Removal of different contaminants requires different types of treatment. Because surface water is affected by runoff, which can pick up many contaminants, more extensive treatment is necessary than for groundwater.
Filtration of surface water removes not only particulate matter, but also certain disease-causing microorganisms. There are many methods of filtration, including:
- Conventional (coagulation, flocculation, sedimentation, and sand filtration);
- Cartridge; and
- Diatomaceous earth.
Because some microorganisms can pass through filters, water can also be treated through disinfection. Chlorine is the most common compound for this purpose, but ultraviolet light can be used for disinfecting water, as can ozone and other oxidants.
For chemical contaminant removal, other water treatment methods can be employed, such as:
- Granular activated carbon beds;
- Reverse osmosis;
- Ion exchange; and
These treatments are often expensive and used only if there are no alternate, cleaner sources of water.
Many community water supplies also add fluoride to their water for the benefit of reduced dental decay. Iron removal systems and softening are among treatments available to address aesthetic factors such as taste, odor, and iron staining.
After the water is treated, a network of pipes transports it to customers. Flow through the pipes depends on consumer demand, and is accomplished either by gravity or with the use of pumps. Water storage tanks are placed in the distribution network so that water can be stored during times of low usage, and more water can be available during times of high use.
When a faucet is turned on, water flows from the storage tanks through pipes into the home. When water in the tank gets low, more water is pumped from the water source (either surface water or groundwater) and into the tank. Storage tanks also provide extra water in case of an emergency, such as a fire.
Water Protection and Conservation
Because all water on the planet Earth is a part of the continuing hydrologic cycle , the amount of water on the planet can neither increase nor decrease. However, as the human population grows, demand for clean water increases. As developments expand into previously undeveloped areas, the potential for water pollution also increases. New, clean, and safe sources of water are getting more and more difficult to find. Therefore, it is especially important to protect and conserve existing water supplies.
Households, businesses, farmers and ranchers, and industries all must alter water use to help conserve the existing water now available. Organizations and individuals are switching to water-efficient appliances and practices, and more responsible irrigation and processing techniques. Also, with urban areas getting closer and closer to rural land, multiple land uses are in close proximity. Use of fertilizers and pesticides on agricultural and residential land, runoff from pavement with automobile fluid leaks, domestic wastewater discharges, and industrial wastewater all affect water quality. It is important that these practices are carefully managed so that the affect on water quality is minimized, in order to secure sufficient and safe water supplies for the future.
SEE ALSO C ONSERVATION , W ATER ; D RINKING -W ATER T REATMENT ; G ROUNDWATER ; R AINWATER H ARVESTING ; R ECLAMATION AND R EUSE ; S AFE D RINKING W ATER A CT ; S PRINGS ; S UPPLIES , P ROTECTING P UBLIC D RINKING -W ATER ; W ATER WORKS , A NCIENT .
American Water Works Association. Water Quality and Treatment: A Handbook of Community Water Supplies, 5th ed. New York: McGraw-Hill, 1999.
Salvato, Joseph A . Environmental Engineering and Sanitation. New York: John Wiley& Sons, 1982.
U.S. Environmental Protection Agency. Drinking Water and Health: What You Need to Know. Office of Groundwater and Drinking Water, EPA 816-K-99-001 (1999).
Ground Water and Drinking Water. U.S. Environmental Protection Agency, Office ofWater. <http://www.epa.gov/safewater> .
IS BOTTLED WATER BETTER?
Bottled water, including bottled mineral water, is an enormous business in the United States, where it is regulated by U.S. Food and Drug Administration. The source for bottled water must be approved, and is usually a spring, well, or public water supply. The label must identify the source of the water, as well as certain nutritional information.
Water to be bottled often is treated with additional methods that remove chlorine or disagreeable tastes and odors. The federal monitoring requirements are not as complete, nor as stringent, as those for public water supplies.
Even though bottled water can cost up to 1,000 times as much as tap water, many people find that bottled water tastes better than water from the tap. Moreover, bottled water is convenient when traveling to areas of questionable water quality, or when participating in activities away from home.