Background (Encyclopedia of Global Resources)
Although water could exist on the Earth without life, life could not exist without water. It is the most abundant liquid on the Earth. In its solid and liquid forms, water covers about 70 percent of the Earth’s surface. It exists in gaseous form as water vapor in the lower atmosphere, varying from close to 0 percent to about 4 percent by volume from region to region. Water constitutes most of the living tissue in humans: about 92 percent of blood plasma, 80 percent of muscle tissue, 60 percent of red blood cells, and more than 50 percent of most other tissues.
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Water Properties (Encyclopedia of Global Resources)
Water is a compound of two atoms of hydrogen and one of oxygen, giving it the well-known chemical formula H2O. It has some unique properties. It can exist naturally in three states on Earth: solid, liquid, and gaseous. Furthermore, under normal pressure, when heated from 0° Celsius, the melting point of water, to 4° Celsius, it contracts and reaches its highest density. This unusual thermal condition contrasts sharply with most other substances, which expand and experience decreasing density when they are heated. Therefore, ice is less dense than water and will float. This property has substantial implications, as it allows water to freeze from the surface downward, thereby allowing circulation to continue under the frozen surface so that fish can survive. Submarines that travel under the Arctic Ocean ice pack could not do so were it not for water’s unusual thermal property.
Water is an excellent solvent, so much so that “pure water” is hard to find in nature. Water has the highest specific heat of all common substances. Specific heat is the amount of heat that a fluid needs to raise the temperature of a unit volume by 1 degree. This is an important property, as the enormous heat capacity of water has an equalizing effect on the Earth’s climate. Maritime locations have a milder climate than those that are located in continental interiors. Thus, the average annual temperature range between the warmest and coldest...
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Distribution of Water (Encyclopedia of Global Resources)
Earth is a well-watered planet. Thus, hypothetically, if the entire surface of the Earth could be leveled off and the ocean depths filled with the continents, the planet would be covered with water to a depth of more than 3 kilometers. By far, most of the world’s water (97 percent) is contained in the oceans. Another 2 percent is locked in ice caps and glaciers. This means that almost all the water in the world (99 percent) is either salty or frozen. The remaining water is accounted for by groundwater to a depth of 4 kilometers, freshwater lakes, saline lakes and inland seas, soil moisture and water in the unsaturated zone, and the atmosphere. Finally, if one measured the average volume of all the rivers on Earth, the estimated amount would only be 0.0001 percent of the total water on the planet.
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Water as a Resource (Encyclopedia of Global Resources)
There are several characteristics that pertain to water as a resource. First, water is a renewable resource. As governed by the hydrologic cycle, it is continuously going through the processes of evaporation, convection, and advection in the atmosphere; precipitation; interception and transpiration by vegetation; overland flow; infiltration and percolation through the soil and unsaturated zone to the groundwater in shallow, intermediate, and deep aquifers; and base flow from groundwater to streams for eventual transport to the ultimate sink on Earth, the oceans. In the oceans, it evaporates again to continue the cycle. The quantity of water on Earth is relatively fixed, although the quality is affected by numerous anthropogenic activities.
Second, water is ubiquitous on the Earth. It can be found almost anywhere, although it may be too salty or frozen to use directly. Available and abundant freshwater resources, like mineral resources, are unevenly distributed. Thus, water must be transported long distances to supply the needs of major metropolitan areas. For example, New York City gets most of its water from Delaware River basin reservoirs, some 200 kilometers away. Los Angeles depends on water that is transported hundreds of kilometers from Northern California, the Owens Valley east of the Sierras, and the Colorado River.
Third, water can be considered a common property that has poorly defined property rights....
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Water Use (Encyclopedia of Global Resources)
The various ways that water is used can be dichotomized into offstream and instream use. Offstream use pertains to water that is diverted (withdrawn) from surface water or groundwater sources and transported to the place of use. This includes water that is used for domestic, commercial, irrigation, livestock, industrial, mining, and thermoelectric power purposes. Each of these seven categories of offstream water use has a different effect on the potential for reuse of the return flows. For example, the return flow for irrigation is often contaminated by pesticides, herbicides, salts, and fertilizers to such an extent that it has minimal reuse potential. An unfortunate illustration of this situation occurs on the lower Colorado River near Yuma, Arizona, where the United States built a large desalinization plant in order to reduce the salinity of the water for the irrigated areas in nearby Mexico. The plant opened in 1992 and has experienced numerous operating problems. In contrast, the reuse potential of most of the water discharged from thermoelectric plants is high, because the major change in the water is an increase of temperature.
Instream water use occurs without the water being diverted from surface or groundwater sources. These uses include navigation, low flow maintenance to benefit aquatic ecosystems, hydroelectric power generation, and wastewater assimilation. Although instream uses have an impact on the quality and...
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Water Disputes (Encyclopedia of Global Resources)
Because water is essential for life, disputes over its use not only are numerous but also have been going on for several thousand years. In arid areas, such as the Middle East, water is crucial for irrigated agriculture. Thus, Turkey’s decision to build reservoirs for irrigation in the headwaters of the Tigris and Euphrates rivers, which are in its territory, may deprive the downstream states Iraq and Syria of water on which they have come to depend. The allocation of the waters of the Jordan River among the neighboring states of Israel, Jordan, Lebanon, and Syria in another politically sensitive and drought-prone area is related to the viability of peace in the region. With the small exception of some limited reserves of groundwater that accrued from ancient pluvial periods, Egypt is totally dependent on the Nile River, which originates in Ethiopia and Lakes Albert and Victoria in east-central Africa. Any large diversion of the Nile by the upstream states would have a major impact on Egypt.
The Colorado River and its tributaries begin in the Rocky Mountains in Wyoming, Colorado, and New Mexico and flow for 2,333 kilometers through Utah, Arizona, Nevada, and California before emptying into the Gulf of California in Mexico. Although agreements exist among the seven states and Mexico regarding water allocation, problems have developed and are likely to worsen in the future, because the initial allocation was predicated on an...
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Water Quality (Encyclopedia of Global Resources)
Until relatively recently, societies were more concerned with water quantity than with water quality. However, this began to change as growing concentrations of industry and increased population density led to larger amounts of impurities being released into local water sources. By the end of the nineteenth century, the Thames River near London and other rivers near large European cities were so polluted that the rivers became anaerobic (containing no dissolved oxygen) and emitted offensive odors. Fish could not survive in these waters. It became obvious that wastewater from residential and commercial sources had to be treated prior to release into a receiving watercourse.
One solution to the problem in urban areas has been to construct public sewers that connect to wastewater treatment plants, which have helped to improve water quality. In more rural areas, septic systems and well-constructed latrines are generally used to handle wastewater. However, there are countries where unimproved sanitation facilities, such as public and open-pit latrines, are used by large segments of the population. Thus, access to improved sanitation for the total population (urban and rural) varies from an estimated low of 9 percent for Chad and Eritrea in Africa to 100 percent for such countries as Canada, Israel, Japan, and the United States.
The types of water pollution can be categorized on the basis of their effect on human health and...
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Further Reading (Encyclopedia of Global Resources)
Brooks, Kenneth N. Hydrology and the Management of Watersheds. 3d ed. Ames: Iowa State University Press, 2003.
Cech, Thomas V. Principles of Water Resources: History, Development, Management, and Policy. 2d ed. Hoboken, N.J.: John Wiley & Sons, 2005.
Chapelle, Frank. Wellsprings: A Natural History of Bottled Spring Waters. New Brunswick, N.J.: Rutgers University Press, 2005.
Clarke, Robin, and Jannet King. The Water Atlas. New York: New Press, 2004.
De Villiers, Marq. Water: The Fate of Our Most Precious Resource. Boston: Houghton Mifflin, 2000.
Gleick, Peter H., et al. The World’s Water, 2008-2009: The Biennial Report on Freshwater Resources. Washington, D.C.: Island Press, 2009.
Glennon, Robert Jerome. Water Follies: Groundwater Pumping and the Fate of America’s Fresh Waters. Washington, D.C.: Island Press, 2002.
Hunt, Constance Elizabeth. Thirsty Planet: Strategies for Sustainable Water Management. New York: Zed Books, 2004.
Hutson, Susan S., et al. Estimated Use of Water in the United States in 2000. Reston, Va.: U.S. Geological Survey, 2004.
Manning, John C. Applied Principles of Hydrology. Illustrated by Natalie J. Weiskal. 3d ed. Upper Saddle River, N.J.: Prentice Hall, 1997.
Powell, James L. Dead Pool: Lake Powell, Global Warming, and the Future of Water...
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Water (Encyclopedia of Science)
Water is an odorless, tasteless, transparent liquid that appears colorless but is actually very pale blue. The color is obvious in large quantities of water such as lakes and oceans. Water is the most abundant liquid on Earth. In its liquid and solid (ice) form, it covers more than 70 percent of Earth's surfacen area called the hydrosphere.
Earth's supply of water is constantly being replaced through a natural cycle called the hydrologic cycle. Water is continually evaporating from the surface of the planet, condensing in the atmosphere, and falling back to the surface as precipitation.
It is impossible to overstate the importance of water to almost every process on Earth, from the life processes of the lowest bacteria to the shaping of continents. Water is the most familiar of all chemical compounds known to humans. In fact, the human body is composed mainly of water.
Chemical properties of water
Water is a single chemical compound whose molecules consist of two hydrogen atoms attached to one oxygen atom. The chemical formula of this compound is H2O. Considering that a hydrogen atom weighs only about one-sixteenth as much as an oxygen atom, most of the weight in water is due to oxygen: 88.8 percent of the weight is oxygen and 11.2 percent is hydrogen. This percentage remains the same from a single water...
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Water (World of Earth Science)
Water is a chemical compound composed of a single oxygen atom bonded to two hydrogen atoms (H2O) that are separated by an angle of 105°. Because of their polar covalent bonds and this asymmetrical bent arrangement, water molecules have a tendency to orient themselves in an electric field, with the positively charged hydrogen toward the negative pole and the negatively charged oxygen toward the positive pole. This tendency results in water having a large dielectric constant, which is responsible for making water an excellent solvent. Water is therefore referred to as the universal solvent. Water can be reused indefinitely as a solvent because it undergoes almost no modification in the process.
Because mineral salts and organic materials can dissolve in water, it is the ideal medium for transporting products of geochemical weathering as well as life-sustaining minerals and nutrients into and through animal and plant bodies. Brackish and ocean waters may contain large quantities of sodium chloride as well as many other soluble compounds leached from Earth's crust.
The concentration of mineral salts in ocean water is about 35,000 parts per million. Water is considered to be potable (drinkable) only if it contains less than 500 parts per million of salts.
Hydrogen bonding, which joins water molecule to water molecule, is responsible for other properties that make water a unique substance. These properties include its large heat capacity, which causes water to act as a moderator of temperature fluctuations due to variations in solar illumination, its high surface tension (due to cohesion among water molecules), and its adherence to other substances, such as the walls of a vessel (due to adhesion between water molecules and the molecules of a second substance). The high surface tension makes it possible for surface-gliding insects and broad, flat objects to be supported on the surface of water. Adhesion of water molecules to soil particles is the primary mechanism by which water moves through unsaturated soils.
Hydrogen bonding is also responsible for ice being less dense than water. If ice did not float, all bodies of water would freeze from the bottom up, becoming solid masses of ice and destroying all life in them. In addition, from season to season, frozen water bodies would remain frozen, resulting in large changes in climate and weather, such as decreased precipitation due to reduced evaporation. Ice floats because as the temperature of water is lowered the tendency of water to contract as its molecular motion decreases is overcome by the strength of hydrogen bonding between molecules. At 4°C (39°F), water molecules start to structure themselves directionally along the lines of the hydrogen bonds, at angles of 105° As the temperature drops toward 0°C (32°F), spaces develop between the lines until the open, crystalline form characteristic of ice develops. Its openness produces a density slightly less than that of liquid water, and ice floats on the surface, with approximately nine-tenths submerged.
Water is the only common substance that occurs naturally on earth in three different physical states. The solid state, ice, is characterized by a rigid crystalline structure occurring at or below 0°C (32°F) and occupying a definite volume (found as glaciers and ice caps, as snow, hail, and frost, and as clouds formed of ice crystals). At sea level atmospheric pressure, the liquid state exists over a definite temperature range 0°C to 100°C (32 to 212°F), but is not rigid nor does it have a particular shape. Liquid water has a definite volume but assumes the shape of its container. Liquid water covers three-fourths of Earth's surface in the form of swamps, lakes, rivers, and oceans as well as found as rain clouds, dew, and ground water. The gaseous state of water (water vapor) neither occupies a definite volume nor is rigid because it takes on the exact shape and volume of its container. Water vapor (liquid water molecules suspended in the air) occurs in steam, humidity, fog, and clouds.
During phase changes, one phase does not suddenly replace its predecessor as the temperature changes, but for a time at the melting or boiling point, two phases will coexist. As water changes from the gaseous form to the liquid form, it gives off heat at about 540 calories per gram, and as it changes from the liquid form to the solid form, it gives off about 80 calories per gram. The turbulence of thunderstorms is in large part due to the release latent heat of water especially as water condenses into water droplets or into crystals of ice (i.e., hail).
Pressure affects the transition temperature between phases. For example, at pressures below atmospheric, water boils at temperatures under 100°C (212°F), therefore food takes longer to cook at higher elevations.
Water is a major geologic agent of change for modifying Earth's surface through erosion by water and ice.
See also Acid rain; Atmospheric chemistry; Chemical bonds and physical properties; Chemical elements; Clouds and cloud types; Condensation; El Nino and La Nina phenomena; Erosion; Evaporation; Freezing and melting; Freshwater; Rate factors in geologic processes
Water (Encyclopedia of Food & Culture)
Water (How Products are Made)
Water is a chemical compound needed by most plants and animals on Earth in order to sustain life. Pure water is a tasteless, odorless, transparent liquid. In small amounts it is colorless, but it takes on a bluish tint in larger amounts. Water is an excellent solvent and as a result it usually contains a wide variety of dissolved minerals and other chemicals. It can also carry and support bacteria. Most of the water distributed through municipal water systems is treated to remove harmful substances. Some bottled waters undergo even further treatment to remove almost all impurities. The English word water is derived from the German word wasser, which in turn is derived from an ancient Indo-European word meaning to wet or wash.
The controlled use of water dates to at least 8,000 B.C. when farmers in Egypt and parts of Asia trapped floodwaters for crop irrigation. The concept of using irrigation canals to bring water to crops, rather than waiting for a flood, was first developed about 2,000 B.C. in Egypt and Peru. By about 1,000 B.C., the city of Karcho, in what is now Jordan, built two aqueducts to bring an adequate supply of water for the city's population. This is the first recorded instance of a planned municipal water supply.
Early water treatment was surprisingly advanced, although rarely practiced. An ancient Sanskrit manuscript, from what is now India, advises that drinking water should be kept in copper vessels, exposed to sunlight, and filtered through charcoal. Ancient Egyptian inscriptions give similar advice. Many of these methods are still used today. In about 400 B.C., the Greek medical practitioner Hippocrates suggested that water should be boiled and strained through a piece of cloth. Despite these early references, most people drank untreated water from flowing streams or subterranean wells. As long as there were no sources of contamination nearby, this was a satisfactory solution.
As the population of Europe and other parts of the civilized world grew, their sources of water became increasingly contaminated. In many cities, the rivers that served as the primary sources of drinking water were so badly contaminated with sewage that they resembled open cesspools. Cholera, typhoid, and many other water-borne diseases took their toll. In 1800, William Cruikshank of England demonstrated that small doses of chlorine would kill germs in water. By the 1890s, several municipalities found that slowly filtering water through beds of sand could also significantly reduce the incidence of disease. The public outcry for safe drinking water reached such a crescendo that by the early 1900s most major cities in the United States had installed some sort of water treatment system.
Even with water treatment, water contamination remained a serious concern as an increasing amount of industrial wastes poured into the nation's rivers and lakes. As the adverse health effects of lead, arsenic, pesticides, and other chemicals became known, the United States federal government was obliged to pass the Water Pollution Control Act of 1948. This was the first comprehensive legislation to define and regulate water quality. It was followed by a series of increasingly tougher requirements, culminating in the current Environmental Protection Agency (EPA) water quality standards. In addition to the federal standards, most states have their own water quality laws, and some state laws are more stringent than those specified by the EPA.
Types of Water
Pure water is an almost non-existent entity. Most water contains varying amounts of dissolved minerals and salts, plus an abundance of suspended particles such as silt and microscopic organic material. Different types of water are classified by the presence or absence of these impurities.
Tap water, or municipal water, has under-gone a series of treatments to kill harmful bacteria, remove sediments, and eliminate objectionable odors. It may also have had one or more chemicals added for a variety of reasons.
Hard water contains high amounts of calcium and magnesium salts. This causes soap to form curds. Hard water is further divided into temporarily hard water and permanently hard water. Temporarily hard water contains bicarbonates of calcium and/or magnesium, which react to form a hard substance called scale when the water is heated. Scale can clog hot water heaters and pipes and leave deposits on cooking utensils. Permanently hard water contains sulphates, chlorides, or nitrates of calcium and/or magnesium, which are not affected by heating. Soft water contains relatively low amounts of calcium and magnesium salts, although the definition of "low" varies. The term "softened water" refers to hard water that has had enough salts chemically removed to avoid forming soap curds. It is high in sodium chloride.
If water contains a large quantity of dissolved minerals, it is called mineral water. Mineral waters can be divided into five main classes: saline, alkaline, ferrunginous, sulphurous, and potable. Saline water has a high level of sodium or magnesium sulphate or sodium chloride. Alkaline water has a high concentration of salts which give it a pH in the range of about 7.2-9.5, where a pH of 7 is neutral and a pH of 14 is highly alkaline. Ferrungious water is rich in iron, which gives it a rusty color. Sulphurous water is rich in sulphur compounds and is distinguished by its rotten egg smell. Potable water has a mineral content of less than 500 parts per million and is most commonly bottled and sold as a specialty drinking water.
Carbonated water, soda water, and sparkling water all contain dissolved carbon dioxide. This may occur naturally where limestone or other carbonate rocks are present, or the carbon dioxide may be added artificially under pressure.
Spring water and artesian water are distinguished only by the fact that they flow from the ground naturally without the aid of drilling or pumping. Otherwise, there is nothing that makes them different than water from other sources.
Distilled water has been purified by an evaporation-condensation process that removes most, but not all, impurities. Deionized water has been purified by an ion-exchange process, which removes both positive ions, such as calcium and sodium, and negative ions, such as chlorides and bicarbonates. It is sometimes called de-mineralized water. Purified water is municipal water that has undergone carbon filtration, distillation, deionization, reverse osmosis, ultraviolet sterilization, or some combination of these processes to remove almost all minerals and chemical elements, both good and bad.
A water molecule consists of two atoms of hydrogen bonded to one atom of oxygen. The chemical symbol is H2O. Water usually also contains a wide range of organic and inorganic materials in solution or suspension.
In the process of treating water for use in a municipal system, several chemicals may be added. These include disinfectants like chlorine, chloramine, or ozone; coagulantants like aluminum sulfate, ferric chloride, and various organic polymers; acidity neutralizers like caustic soda or lime; and chemicals to help prevent tooth decay in the form of various fluoride compounds.
The Treatment Process
The specific water treatment process depends on the intended application. Some water, such the water used to irrigate crops,
Here is a typical series of operations used to treat municipal water for distribution to homes and businesses.
- 1 Most municipal water comes from two sources: ground water and surface water. Most ground water is tapped by drilling wells into the underground water-bearing layer called the aquifer. Some ground water rises naturally in the form of springs. Surface water is tapped by impounding rivers behind dams. The surrounding area that drains into the rivers is called the watershed. In many cases, access to and use of the watershed is limited to prevent contamination of the runoff water.
- 2 From the well or dam, the water is carried to the water treatment plant in open canals or closed pipes. In some cases, the water supply is close to the municipality. In other cases, the water has to be transported many hundreds of miles (km) to reach its destination. Sometimes the water is stored in intermediate reservoirs along the way to ensure that there will always be an adequate supply available to meet a city's fluctuating needs.
- 3 In some water treatment plants, the water is initially disinfected by contact with ozone-rich air in a series of chambers. This step is used by most plants in Europe, but only a few plants in the United States. Ozone (03) is formed by passing compressed air through a high-voltage electric arc. This causes some of the oxygen (02) molecules in the air to split in half and reattach themselves to other oxygen molecules to form ozone. Ozone effectively kills most germs and also destroys compounds, which cause unpleasant tastes and odors. It has a relatively short life, however, and does not remain in the water to protect it during storage and distribution. For this reason, a small dose of chlorine or chloramine is added to the water at the end of the treatment process.
- 4 The water then passes through a flash mixer where chemicals known as coagulants are rapidly mixed with the water. The coagulants alter the electric charge around any suspended particles in the water and make them attract each other and clump together, or coagulate.
- 5 The water moves slowly through a series of chambers where it is gently mixed by the swirling flow. As the water mixes, the charged particles continue to bump into each other and form even larger particles called flocs.
- 6 The water flows into a settling basin or tank where the heavy flocs sink to the bottom. Some settling basins have two levels to double their capacity. The material that settles to the bottom is vacuumed out of the basin with a device like a pool vacuum and is deposited in a solids holding basin. The trapped material from the filter (step 7) is also added to the solids holding basin. These combined materials are sent through a gravity thickener and then a press where most of the water is squeezed out. The remaining solids are loaded into trucks and transported to a landfill for disposal.
- 7 The partially cleaned water passes through several layers of sand and pulverized coal, which trap any very small particles that remain in the water. Some harmful organisms are also trapped this way in those water treatment plants that do not use ozone as an initial disinfectant. The filter layers are back-flushed periodically to remove the trapped material.
- 8 In some plants, the water is passed through a bed of activated charcoal granules. Chemical contaminants in the water stick to the surface of the charcoal in a process known as carbon adsorption.
- 9 In some areas where the water contains undesirable amounts of iron and manganese or certain dissolved gases, the water is sprayed into the air from large basins to aerate it. When the water mixes with the air, it picks up oxygen, which causes some of the contaminants to settle out. Other contaminants are removed by evaporation.
- 10 In some water treatment plants, a fluoes ride compound is added to the water to help prevent tooth decay. Fluoride occurs naturally in some water supplies and additional amounts are not required. In the past, fluoridation has been a hotly debated subject, and not every municipality adds fluoride to their water.
- 11 Other chemicals may be added to the water to help reduce corrosion in pipes and plumbing fixtures. This is done by adding controlled amounts of certain chemicals to adjust the pH factor to a neutral level.
- 12 As the water leaves the treatment plant, it receives a small dose of chlorine or chloramine to kill any harmful bacteria that may have found their way into the distribution system. If the plant does not use ozone as an initial disinfectant, a larger amount of chlorine or chloramine is added to the water.
- 13 After the water leaves the plant, it is usually stored in covered tanks or reservoirs to protect it from contamination. In some areas, these storage facilities are located at a higher elevation than the surrounding terrain, and the water is pumped up into the tank or reservoir. This elevated storage position provides the pressure necessary for adequate flow through the water mains and pipes within the city. In other cases, the water is stored in ground-level facilities, and the pressure is supplied by electric pumps that run on demand.
The federal and state water quality standards set maximum contamination levels for more than 90 organic, inorganic, microbiological, and radioactive materials that may be found in water. These standards are further divided into primary standards, which cover materials that may be harmful to humans, and secondary standards, which cover materials and properties that may affect aesthetic qualities such as taste, odor, and appearance. A typical water district may perform more than 50,000 chemical and bacteriological analyses of the water supply each year to ensure the standards are being met.
The public's concern over safe drinking water is expected to result in even more stringent water quality standards in the future. Ironically, one of the most recent concerns is not about outside contamination, but about the effects of one of the substances commonly used to disinfect waterhlorine. Studies within the last 30 years have shown that chlorine forms certain compounds with the organic materials found in water. The most common compounds are called trihalomethanes, or THMs, which have a 1-in-10,000 risk of causing cancer when ingested or inhaled over a long period. One alternative to using chlorine is chloramine, which is a combination of ammonia and chlorine that does not form THMs as readily. Many water treatment plants have already switched to chloramine. Other alternative disinfectants include ozone, ultraviolet light, chlorine dioxide, and a hybrid of ozone and hydrogen peroxide called peroxone.
Where to Learn More
von Wiesenberger, Arthur. H2O: The Guide to Quality Bottled Water. Woodbridge Press, 1988.
Water Quality Standards Handbook, 2nd edition. United States Environmental Protection Agency, 1994.
Arrandale, T. "A Guide to Clean Water." Governing (December 1995): 57-60.
Wasik, J. F. "How Safe is Your Water?" Consumers Digest (May/June 1996): 63-69.
"Alameda County Water District Water Treatment Facility." Pamphlet. Alameda County Water District, 1993.
"Layperson's Guide to Drinking Water." Pamphlet. Water Education Foundation, 1995.
Los Angeles Department of Water and Power. http://www.ladwp.com.