Water Supply Systems

Summary

Water supply systems are designed to provide adequate water to the public for drinking, bathing, washing, and waste disposal. The water comes from surface water contained in aquifers, rivers, lakes, reservoirs, groundwater from subsurface sources, and desalinated seawater. Industrial use and water for irrigation form another large component of the overall water demand. The operators of these systems can be either public or private. To meet government standards for potable drinking water, raw water must be treated with a mix of mechanical, chemical, and biological means before delivery to the customer through an extensive system of pipes.

Definition and Basic Principles

Water supply systems comprise water sources, treatment plants, storage systems, and delivery systems to commercial and residential consumers. These systems involve apparatuses such as pumps, chemical feeds, testing laboratories, and networks of both surface and underground pipes. A water supply facility must be large enough to meet existing and anticipated future water demands within its service area. Water can be withdrawn by public or self-supplied systems such as private wells.

According to the US Environmental Protection Agency (EPA), about 90 percent of Americans get their water from public supply systems. The EPA identifies three different classifications of public water systems. A community water system (CWS) provides water year-round to an established population, from small towns to major urban areas such as New York City, with a system that serves about 9 million people. A non-transient, non-community water system is defined as a system that provides regular water service to twenty-five or more of the same people for six months out of the year or more. This includes institutions such as hospitals, schools, and offices that have their own supply systems. Finally, transient non-community water systems serve people who do not stay long-term, such as a campground or gas station.

There are around 148,000 public water systems in the United States. The smaller systems generally rely on groundwater from local well fields, while larger systems tend to use surface water from lakes, rivers, and reservoirs. Hydrologically, it should be noted that surface water is partially fed from groundwater as base flow that is part of the hydrologic cycle.

A major issue addressed by water supply systems is water quality. Raw water sources vary in quality over time, and operators of water treatment plants must constantly monitor the biochemical changes that can occur in their plant's water sources. Heavy precipitation can quickly increase the suspended material in the stream, requiring aluminum to make flocs (clot-like masses) that can form and settle these materials to the bottom of a holding basin. State and federal laws govern potable water quality for systems of all sizes and purposes. However, water quality standards for industrial uses and irrigation may differ from those for CWSs.

Background and History

The Minoan civilization on the Mediterranean island of Crete about five thousand years ago is believed to have been the first major builder of water supply aqueducts. In China, archaeologists have discovered ancient wells dug to a depth of 1,500 feet. A special form of subsurface tunnel called a qanat was used in the Middle East (especially Iran) and North Africa about 1000 BCE. Aboveground stone aqueducts were started in Rome in 312 BCE, and by 300 BCE, there were fourteen major aqueducts, bringing in about 40 million gallons per day. The estimated daily per capita use in ancient Rome was an astonishing thirty-eight gallons, compared with about two gallons for Paris in medieval times.

In the ninth century, a significant water supply system was built in Córdoba, Spain. An early pump was installed by Dutch engineer Peter Morice at the London Bridge in 1582, and other sixteenth-century systems were located in Hanover, Germany, and Mexico. Pumps and piping systems were installed in London and Paris during the early seventeenth century—the earliest residential service probably occurred in London in 1619. Nevertheless, these systems were limited to large urban locales, and many water sources, from the Middle Ages to the nineteenth century, were usually surface sources (rivers), where waste was commonly dumped. The results were deadly—53,000 people died in London alone during the cholera epidemic of 1848–1849.

Some cities were more advanced, such as Richmond, Virginia, which built slow sand filters to treat its water in 1834. It was generally during this period that the ability of water to deliver diseases caused by bacteria and other pathogens was recognized. As a result, methods of treating water to remove contaminants were developed, from sand-filtration systems starting in the mid-nineteenth century to chlorination, beginning in England in 1897. At this time, water supply systems had also extended beyond the cities to most towns. For example, Jersey City, New Jersey, tried chlorinating raw river water in 1908 and found that the typhoid rate dropped sharply. Consequently, chlorination became a common disinfectant in water treatment plants in the United States and elsewhere.

How It Works

Water Sources. The first part of a water supply system is its source, and generally, there are two—surface sources like rivers and lakes and groundwater from underground aquifers. Many cities are favorably situated on rivers or lakes, such as Cairo on the Nile, Chicago on Lake Michigan, London on the Thames, New Orleans on the Mississippi, Paris on the Seine, and Washington, DC on the Potomac. Other cities in coastal areas could not use saline water and, therefore, had to build expensive inland reservoirs. New York City had to make seven reservoirs in the Croton, Catskill, and Delaware watersheds in New York State to serve the daily consumption needs of 9 million people.

Cities in the southwestern United States face the major problem of population growth without sufficient precipitation for their water supply. For example, the average annual rainfall for Las Vegas and Phoenix is well under ten inches. Yet, the population of these cities grew considerably in the late twentieth and early twenty-first centuries. Consequently, controversy has developed over the large water transfers to California from the other states in the Colorado Basin (Colorado, Wyoming, Utah, New Mexico, Nevada, and Arizona).

Many areas in the United States sit atop extensive permeable formations that contain large amounts of groundwater. The coastal plain province that extends from Cape Cod, Massachusetts, to Florida and continues to the Gulf of Mexico forms a huge repository of groundwater. According to US Geological Survey (USGS) data, New York's Nassau and Suffolk counties had a combined population of 2.5 to 3 million people in the late 2010s, who got all their groundwater from local sources. Florida is noted for extensive amounts of groundwater in its Biscayne and Floridian aquifers. The glaciated areas in the northern portion of the continental United States, approximately above the Ohio and Missouri Rivers, also have favorable supplies of groundwater.

Water Collection and Storage. As part of the hydrologic cycle, a portion of the precipitation that lands on the Earth's surface flows slowly into streams that eventually empty, for the most part, into the ocean. Another portion of the precipitation infiltrates permeable layers of the Earth and is stored as groundwater in subsurface geologic formations called aquifers. This underground storage also flows slowly back into streams as base flow and can account for a good portion of the total flow of a stream. Groundwater can be extracted from underground sources by pumping from one or more wells. In contrast, surface water from one or more intake pipes can be extracted from a stream, lake, canal, or reservoir built to store water. The raw water from surface intake or a well is transported by pipe to the water plant for physical, chemical, and biological treatment to meet mandated standards for potability before distribution.

Water Treatment. The function of all water supply plants is to treat the incoming raw water so that the finished product is safe to use, with drinking water requiring the most careful treatment. Although there are variations in treatment techniques, most facilities start with screens that block large items that may be floating in the raw water (generally surface), which could include debris, dead animals, and fish. The next step is to move the raw water to hold basins designed to settle out suspended sediments such as silt and clay. If the incoming water has large amounts of suspended materials, an additional step called flocculation/coagulation is used, whereby chemicals such as alum and soda ash are added to the water to facilitate fine-particle suspension. This coagulation procedure generates floc, which will get heavy enough to settle in holding tanks as sludge over time. About 90 to 99 percent of the viruses that may be in the water are removed by this procedure.

The next step is to let the partially treated water filter through layers of sand and gravel to remove finer particles that may remain. These filters eventually get clogged with sediments, necessitating backwashing or flushing removal, leaving a residue that ultimately ends up in a sewage plant for additional treatment.

Fluoridation and chlorination generally form the final stages of the water treatment process. A commonly used compound, which is recommended for maintaining healthy teeth, is sodium fluoride. In 1945, Grand Rapids, Michigan, was the first city to add fluoride to drinking water. From 2005 to the early 2020s, 66 to 70 percent of US residents lived in communities with water supplies that were fluoridated at an acceptable concentration level. Chlorination is a common disinfection method used since the turn of the twentieth century to kill residual bacteria and some viruses by adding chlorine gas to the finished water. Some people do not like the taste or smell of chlorinated water, but adding activated carbon into the treatment process can make the water more palatable. One of the benefits of chlorination is that residual amounts of chlorine can remain in the treated water as it travels many miles in the system. The disinfected water travels with the flow until it reaches all the customers. Though scientific evidence shows these water treatments to be safe for drinking and beneficial for human mouths, some oppose their inclusion in public water. Groups like the Fluoride Action Network began forming in the late 2010s in opposition to fluoride in drinking water, rallying to have it removed.

Some water utilities use ozone-gas and ultraviolet-light systems as alternatives for killing any residual bacteria and viruses that may still be present in this last stage of water treatment. Ozone is noted as being a strong oxidant of taste and odor compounds in addition to being a very effective disinfectant. However, it is more expensive than chlorine and does not have the same ability to continue as a disinfectant as it leaves the treatment plant to a household that may be miles away at the end of the distribution system. Ultraviolet (UV) light is very effective in killing almost all of the microbiological organisms that may have slipped through earlier steps in treatment, as the light energy is absorbed in the DNA of the microbes, therefore ending reproduction at the cellular level. UV usage is both expensive and slow, but in select situations, it can be very useful.

Desalination. Many places in the world border oceans. The saltwater is acceptable for shipping and tourism but not for drinking water. Seawater has total dissolved solids (TDS) of about 35,000 parts per million (ppm), vastly greater than the US safe drinking water standard for TDS of 500 ppm. Most of the desalination plants in the world are found in the Middle East, particularly those countries on the Arabian Peninsula, which have a mean annual precipitation of fewer than twelve inches.

One immediate drawback of desalination is that the process requires huge amounts of energy. Desalination expenses are several times that of filtering freshwater. The techniques that have been tried include heat distillation, chemical (ion exchange) or electrical (ion removal) procedures, freezing, solar humidification, and reverse osmosis (forcing seawater through a semipermeable membrane).

Water Distribution Systems. In industrialized developed countries, the infrastructure for delivering potable water to the public, commercial users, and industries includes groundwater wells, intakes for surface water, reservoirs (if available), treatment plants, storage tanks, and an extensive network of pipes. The plants, storage tanks, pipes, and pumps will vary in size based on the expected demand from customers, plus a safety factor for fires and emergencies. Treated water can be stored underground or in aboveground tanks. Water storage is necessary to allow sufficient time for disinfection (chlorine contact time) and to handle peak demand, which typically occurs in the morning as many people shower. The storage facilities within a typical distribution system are designed to hold enough water to meet peak demands that are greater than the maximum daily demand, which is based on 50 percent of the storage capacity of the particular system. In addition, they must have sufficient capacity to handle the demands of specific emergencies, such as a fire or water main break. Most municipal water systems have one or two days' worth of potable water in storage for any kind of emergency that may develop.

It is regrettably apparent that the aforementioned characteristics of a functioning system of treated water and proper distribution to large segments of the population in developing nations are not occurring at the desired and necessary rate. Millions of people are affected by and die from water-related diseases that could be prevented by adequate treatment and functioning delivery systems. Some estimates suggest that 2 million to 5 million deaths per year can be attributed to water-related diseases that mainly affect small children, such as cholera, typhoid, dysentery, and other diseases associated with diarrhea.

Wastewater Treatment. This field is concerned with the proper treatment of sewage. Its relevance and connection to water supply is immediately apparent if one notes that sewage treatment plants commonly discharge their treated wastes into the same rivers that water supply treatment plants use as their water source. Potable water plants can quite easily be found downstream of sewage plants. For example, New Orleans is at the downstream end of the Mississippi, and there are many wastewater plants upstream.

Applications and Products

Water Demand. Only about 5 percent of the finished product of water treatment is used for drinking—the overwhelming majority of the remaining treated water in the United States and Canada is used for toilet flushing and bathing. All the water must meet the same standards, regardless of its use. The requirement that all new toilets installed after 1994 must be low-flush was part of an effort to reduce overall water demand.

The USGS has been estimating the use of water in the United States at five-year intervals since 1950. It depends on water use data from each state as part of its compilation. Water that is distributed to public and private purveyors is used for a variety of domestic, commercial, and industrial purposes. Water distribution also includes public services that may not be billed, such as firefighting, municipal pools and parks, pipe leakage and flushing, and water tower repairs. Around 90 percent of the US population gets their water from a public system regulated by the EPA. More than half of this water is obtained from surface sources (rivers, lakes, and reservoirs), and the remainder is from groundwater sources.

The US population increased from 175 million in 1950 to about 300 million in 2005 and around 333 million in the early 2020s. One would presume that freshwater diversions would have increased at a proportional rate, but the total diversions peaked in 1980. This effect is most probably associated with decreased water diversions for thermoelectric power, which requires large amounts of cooling water.

Careers and Course Work

Careers in water supply occur in a number of fields. The overriding direction is a technical specialty. Numerous occupations fall within the purview of water supply system careers. Some entry-level semi-technical jobs at a water treatment plant may be available to those with an associate's degree. For those who want to start at a more professional level, a bachelor of arts (BA) or bachelor of science (BS) degree in a field such as civil engineering (there are numerous subspecialties and courses in the water resources field), hydrogeology, and geology (groundwater and related geologic subjects), water quality (includes biology and chemistry courses), physical geography (includes courses in geographic information systems and water resources), and the related fields of meteorology and climatology would be required.

Given the increasingly complicated institutional and regulatory aspects of water supply systems, those individuals who might be interested in these aspects should consider environmental planning and law. Simply reading some of the detailed state and federal legislative documents that pertain to water supply issues will provide more information in this area. It is a specialized field that requires someone to take not only appropriate water-related classes but also those dealing with environmental planning, law, and regulatory issues.

Social Context and Future Prospects

Water, like food and air, is an absolute necessity for all humanity, and indeed all life. Therefore, governments and other organizations continue to work to protect this vital resource. Water testing, treatment, and efficient-use technologies continue to improve, bringing the potential of better supply systems and less waste. However, various environmental and human-made challenges make issues of water rights and accessibility ongoing areas of concern.

Global increases in population pose one such challenge, especially in dry regions such as parts of Africa, where inadequate precipitation can result in numerous deaths. The Sahelian zone south of the Sahara Desert in northern Africa experienced a drought that began in 1968 and continued through the mid-1980s, killing about 100,000 people and leaving agriculture and livestock heavily affected. India is an example of a large and highly populated country that has become increasingly industrialized but has run into a list of major water distribution issues. The water distribution systems in many of its cities are in a state of disrepair to the extent that tap water is available for only a few hours a day. According to various reports, tens of thousands of Indians lacked access to safe drinking water supplies or proper sewage and waste disposal in the 2010s and 2020s, despite ongoing improvement efforts.

In other areas, such as the United States, problems occur with existing water supplies becoming depleted and the challenge of supplying adequate water to growing population centers in dry regions. Experts have warned of the impracticality of major cities in desert regions (such as Los Angeles and Las Vegas) and the danger of shrinking aquifers.

Other problems in the better-watered portions of the world include water quality issues such as exotic new contaminants (including prescription-drug residues) that are not treated by standard techniques in most water supply plants. In the first legally enforceable law on drinking water quality, the Biden-Harris Administration introduced a rule as part of the EPA’s PFAS Strategic Roadmap to protect the American public from perfluoroalkyl and polyfluoroalkyl substances (PFAS). PFAS, also known as forever chemicals, are present in much drinking water across North America. This rule requires around 66,000 public drinking water systems across America to inform the public about the contents of their drinking water and meet new standards.

Other global-scale issues also bear on water supply. Perhaps most threatening is climate change, which poses many different risks. Droughts may increase, and some regions are expected to see some degree of desertification, making water access even more scarce. Other areas are at risk of saltwater intrusion into the freshwater supply due to rising sea levels. Human migration and resource strain caused by other elements of global warming also have the potential to overburden existing water supply systems. In light of such risks, many experts agree that water supply issues pose one of humanity's most significant challenges in the twenty-first century.

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