Matthew R. Fisher
Water, air, and food are the most important natural resources to people. Humans can live only a few minutes without oxygen, less thana week without water, and about a month without food. Water also is essential for our oxygen and food supply. Plants breakdown water and use it to createoxygen duringthe process of photosynthesis.
Water is the most essential compound for all living things. Human babies are approximately 75% water and adults are 60% water. Our brain is about 85% water, blood and kidneys are 83% water, muscles are 76% water, and even bones are 22% water. We constantly lose water by perspiration; in temperate climates we should drink about 2 quarts of water per day and people in hot desert climates should drink up to 10 quarts of water per day. Loss of 15% of body-water usually causes death.
Earth is truly the Water Planet. The abundance of liquid water on Earth’s surface distinguishes us from other bodies in the solar system. About 70% of Earth’s surface is covered by oceans and approximately half of Earth’s surface is obscured by clouds (also made of water) at any time. There is a very large volume of water on our planet, about 1.4 billion cubic kilometers (km3) (330 million cubic miles) or about 53 billion gallons per person on Earth. All of Earth’s water could cover the United States to a depth of 145 km (90 mi). From a human perspective, the problem is that over 97% of it is seawater, which is too salty to drink or use for irrigation. The most commonly used water sources are rivers and lakes, which contain less than 0.01% of the world’s water!
One of themost important environmental goals is to provide clean water to all people. Fortunately, water is a renewable resource and is difficult to destroy. Evaporation and precipitation combine to replenish our fresh water supply constantly; however, water availability is complicated by its uneven distribution over the Earth. Arid climate and densely populated areas have combined in many parts of the world to create water shortages, which are projected to worsen in the coming years due to population growth and climate change. Human activities such as water overuse and water pollution have compounded significantly the water crisis that exists today. Hundreds of millions of people lack access to safe drinking water, and billions of people lack access to improved sanitation as simple as a pit latrine. As a result, nearly two million people die every year from diarrheal diseases and 90% of those deaths occur among children under the age of 5. Most of these are easily prevented deaths.
Water is the only common substance that occurs naturally on earth in three forms: solid, liquid and gas. It is distributed in various locations, called water reservoirs. The oceans are by far the largest of the reservoirs with about 97% of all water but that water is too saline for most human uses (Figure 1).Ice caps and glaciers are the largest reservoirs of fresh water but this water is inconveniently located, mostly in Antarctica and Greenland. Shallow groundwater is the largest reservoir of usable fresh water. Although rivers and lakes are the most heavily used water resources, they represent only a tiny amount of the world’s water. If all of world’s water was shrunk to the size of 1 gallon, then the total amount of fresh water would be about 1/3 cup, and the amount of readily usable fresh water would be 2 tablespoons.
Thewater(or hydrologic)cycle shows the movement of water through different reservoirs, which include oceans, atmosphere, glaciers, groundwater, lakes, rivers, and biosphere. Solar energy and gravity drive the motion of water in the water cycle. Simply put, the water cycle involves water moving from oceans, rivers, and lakes to the atmosphere by evaporation, forming clouds. From clouds, it falls as precipitation (rain and snow) on both water and land. The water on land can either return to the ocean by surface runoff, rivers, glaciers, and subsurface groundwater flow, or return to the atmosphere by evaporation ortranspiration(loss of waterby plants to the atmosphere).
An important part of the water cycle is how water varies in salinity, which is the abundance of dissolvedions in water. The saltwater in the oceans is highly saline, with about 35,000 mg of dissolvedions per liter of seawater.Evaporation(where water changes from liquid to gas at ambient temperatures)is a distillation process that produces nearly pure water with almost no dissolved ions. As water vaporizes, itleaves the dissolved ions in the original liquid phase. Eventually,condensation (where water changes fromgas to liquid) forms clouds and sometimes precipitation (rain and snow). After rainwater falls onto land,it dissolves minerals in rock and soil, which increases its salinity. Most lakes, rivers, and near-surface groundwater have arelatively low salinity and are called freshwater. The next several sections discuss important parts of thewater cycle relative to fresh water resources.
Primary Fresh Water Resources: Precipitation
Precipitation levels are unevenly distributed around the globe, affecting fresh water availability (Figure 3). More precipitation falls near the equator, whereas less precipitation tends to fall near 30 degrees north andsouth latitude, where the world’s largest deserts are located. These rainfall and climate patterns are relatedto global wind circulation cells. The intense sunlight at the equator heats air, causing it to rise and cool,which decreases the ability of the air mass to hold water vapor and results in frequent rainstorms. Around30 degreesnorth and south latitude, descending air conditions produce warmer air, which increases its ability tohold water vapor and results in dry conditions. Both the dry air conditions and the warm temperatures ofthese latitude belts favor evaporation. Global precipitation and climate patterns are also affectedby the sizeof continents, major ocean currents, and mountains.
Surface Water Resources: Rivers, Lakes, Glaciers
Flowing water from rain and melted snow on land enters river channels by surface runoff (Figure 4) and groundwater seepage (Figure 5).Riverdischarge describes the volume of water moving through a river channel over time (Figure 6). The relative contributions of surface runoff vs. groundwater seepage to riverdischarge depend on precipitation patterns, vegetation, topography, land use, and soil characteristics. Soonafter a heavy rainstorm, river discharge increases due to surface runoff. The steady normal flow of riverwater is mainly from groundwater that discharges into the river. Gravity pulls river water downhill towardthe ocean. Along the way the moving water of a river can erode soil particles and dissolve minerals. Groundwater also contributes a large amountof the dissolved minerals in river water. The geographic area drained by a river and its tributaries is called adrainage basinorwatershed. The Mississippi River drainage basin includes approximately 40% of the U.S., a measurethat includes the smaller drainage basins, such as the Ohio River and MissouriRiver that help to comprise it. Rivers are an important water resource for irrigation of cropland and drinking water for many cities aroundthe world. Rivers that have had international disputes over water supply include theColorado (Mexico, southwest U.S.), Nile (Egypt, Ethiopia, Sudan), Euphrates (Iraq, Syria, Turkey), Ganges(Bangladesh, India), and Jordan (Israel, Jordan, Syria).
In addition to rivers, lakes can also be an excellent source of freshwater for human use. They usually receive water fromsurface runoff and groundwater discharge. They tend to be short-lived on a geological time-scale becausethey are constantly filling in with sediment supplied by rivers. Lakes form in a variety of ways includingglaciation, recent tectonicuplift (e.g., Lake Tanganyika, Africa), and volcanic eruptions (e.g., Crater Lake, Oregon). People also create artificiallakes (reservoirs) by damming rivers. Large changes in climate can result in major changes in a lake’s size.As Earth was coming out of the last Ice Age about 15,000 yearsago, the climate in the westernU.S. changed from cool and moist to warm and arid, which caused more than 100 large lakes to disappear.The Great Salt Lake in Utah is a remnant of a much larger lake called Lake Bonneville.
Althoughglaciersrepresent the largest reservoir of fresh water, they generally are not used as a watersource because they are located too far from most people (Figure 7). Melting glaciers do provide a natural source of river water and groundwater. During the lastIce Age there was as much as 50% more water in glaciers than there is today, which caused sea level to beabout 100 m lower. Over the past century, sea level has been rising in part due to melting glaciers. If Earth’sclimate continues to warm, the melting glaciers will cause an additional rise in sea level.
Groundwater Resources
Although most people in the world use surface water, groundwater is a much larger reservoir ofusable fresh water, containing more than 30 times more water than rivers and lakes combined. Groundwater is a particularly important resource in arid climates, where surface water may be scarce. In addition, groundwater is the primary water source for rural homeowners, providing 98% of that water demand inthe U.S..Groundwateris water located in small spaces, calledpore space, between mineral grains and fractures in subsurface earth materials (rock or sediment).Most groundwater originates from rain or snowmelt, which infiltrates the ground and moves downward until it reaches thesaturated zone(where groundwater completely fills pore spaces in earth materials).
Other sources of groundwater include seepage from surface water (lakes, rivers, reservoirs,and swamps), surface water deliberately pumped into the ground, irrigation, and underground wastewatertreatment systems (septic tanks).Recharge areasare locations where surface water infiltrates theground rather than running into rivers or evaporating. Wetlands, for example,areexcellent recharge areas. A large area of sub-surface, porous rock that holds water is an aquifer. Aquifers are commonly drilled, and wells installed, to provide water for agriculture and personal use.
Water Use in the U.S. and World
People need water, oftentimes large quantities, to produce the food, energy, and mineral resources they use. Consider, for example, these approximate water requirements for some things people in the developedworld use every day: one tomato = 3 gallons; one kilowatt-hour of electricity from a thermoelectric powerplant = 21 gallons; one loaf of bread = 150 gallons; one pound of beef = 1,600 gallons; and one ton of steel= 63,000 gallons. Human beings require only about 1 gallon per day to survive, but a typical person in aU.S. household uses approximately 100 gallons per day, which includes cooking, washing dishes and clothes,flushing the toilet, and bathing. Thewater demandof an area is a function of the population and other uses of water.
Global total water use is steadily increasing at a rate greater than worldpopulation growth (Figure 10). During the 20th century global population tripled and water demand grew by afactor of six. The increase in global water demand beyond the rate of population growth is due to improvedstandard of living without an offset by water conservation. Increased production of goods and energy entailsa large increase in water demand. The major global water uses are irrigation (68%), public supply(21%), and industry (11%).
Another water resource problem associated with groundwater mining is saltwater intrusion, whereoverpumping of fresh water aquifers near ocean coastlines causes saltwater to enter fresh water zones. The drop of the water table around acone of depressionin an unconfined aquifer can change the direction of regional groundwater flow, which couldsend nearby pollution toward the pumping well instead of away from it. Finally, problems ofsubsidence(gradual sinking of the land surface over a large area) andsinkholes(rapid sinking of the land surface overa small area) can develop due to a drop in the water table.
Water Supply Crisis
Thewater crisisrefers to a global situation where people in many areas lack access to sufficient water, clean water, or both. This section describes the global situation involving water shortages, also calledwater stress. In general, water stress is greatest in areas with very low precipitation (major deserts), large population density (e.g., India), or both. Future global warming could worsen the water crisis by shifting precipitation patterns away from humid areas and by melting mountain glaciers that recharge rivers downstream. Melting glaciers will also contribute to rising sea level, which will worsen saltwater intrusion in aquifers near ocean coastlines.
According to a 2006 report by the United Nations Development Programme, 700 million people (11% of the world’s population) lived with water stress. Most of them live in the Middle East and North Africa. By 2025, the report projects that more than 3 billion people (about 40% of the world’s population) will live in water-stressedareas with the large increase coming mainly from China and India. The water crisis will also impact food production and our ability to feed the ever-growing population. We can expect future global tension and even conflict associated with water shortages and pollution. Historic and future areas of water conflict include the Middle East (Euphrates and Tigris River conflict among Turkey, Syria, and Iraq; Jordan River conflict among Israel, Lebanon, Jordan, and the Palestinian territories), Africa (Nile River conflict among Egypt, Ethiopia, and Sudan), Central Asia (Aral Sea conflict among Kazakhstan, Uzbekistan, Turkmenistan, Tajikistan, and Kyrgyzstan), and south Asia (Ganges River conflict between India and Pakistan).
Sustainable Solutions to the Water Supply Crisis?
The current and future water crisis described above requires multiple approaches to extending our freshwater supply and moving towards sustainability. Some of the longstanding traditional approaches includedams and aqueducts.
Reservoirsthat form behind dams in rivers can collect water during wet times andstore it for use during dry spells. They also canbe used for urban water supplies. Other benefits of dams and reservoirs arehydroelectricity, flood control, and recreation. Some of the drawbacks are evaporative loss of waterin arid climates, downstream river channel erosion, and impact on the ecosystem including a change froma river to lake habitat and interference with migration and spawning of fish.
Aqueductscan move water fromwhere it is plentiful to where it is needed. Aqueducts can be controversial and politicallydifficult especially if the water transfer distances are large. One drawback is the water diversion can causedrought in the area from where the water is drawn. For example, Owens Lake and Mono Lake in centralCalifornia began to disappear after their river flow was diverted to the Los Angeles aqueduct. Owens Lakeremains almost completely dry, but Mono Lake has recovered more significantly due to legal intervention.
One method that can actually increase the amount of fresh water on Earth isdesalination, whichinvolves removing dissolved salt from seawater or saline groundwater. There are several ways to desalinateseawater including boiling, filtration, and electrodialysis. All of these procedures are moderatelyto very expensive and require considerable energy input, making the water produced much more expensivethan fresh water from conventional sources. In addition, the process creates highly saline wastewater, whichmust be disposed of and creates significant environmental impact. Desalination is most common in the Middle East, where energy from oil is abundantbut water is scarce.
Conservationmeans using less water and using it more efficiently. Around the home, conservation caninvolve both engineered features, such as high-efficiency clothes washers and low-flow showers and toilets, aswell as behavioral decisions, such as growing native vegetation that require little irrigation in desert climates,turning off the water while you brush your teeth, and fixing leaky faucets.
Rainwater harvestinginvolvescatching and storing rainwater for reuse before it reaches the ground. Another important technique isefficient irrigation,which is extremelyimportant because irrigation accounts for a much larger water demand than public water supply. Waterconservation strategies in agriculture include growing crops in areas where the natural rainfall can supportthem, more efficient irrigation systems such as drip systems that minimize losses due to evaporation, no-tillfarming that reduces evaporative losses by covering the soil, and reusing treated wastewater from sewagetreatment plants. Recycled wastewater has also been used to recharge aquifers.
The global water crisis also involves water pollution. For water to be useful for drinking and irrigation, it must not be polluted beyond certain thresholds. According to the World Health Organization, in 2008 approximately 880 million people in the world (or 13% of world population) did not have access to safe drinking water. At the same time, about 2.6 billion people (or 40% of world population) lived without improved sanitation, which is defined as having access to a public sewage system, septic tank, or even a simple pit latrine. Each year approximately 1.7 million people die from diarrheal diseases associated with unsafe drinking water, inadequate sanitation, and poor hygiene. Almost all of these deaths are in developing countries, and around 90% of them occur among children under the age of 5 (Figure 1). Compounding the water crisis is the issue of social justice; poor people more commonly lack clean water and sanitation than wealthy people in similar areas. Globally, improving water safety, sanitation, and hygiene could prevent up to 9% of all disease and 6% of all deaths.
In addition to the global waterborne disease crisis, chemical pollution from agriculture, industry, cities, and mining threatens global water quality. Some chemical pollutants have serious and well-known health effects, whereas many others have poorly known long-term health effects. In the U.S. currently more than 40,000 water bodies fit the definition of “impaired” set by EPA, which means they could neither support a healthy ecosystem nor meet water quality standards. In Gallup public polls conducted over the past decade Americans consistently put water pollution and water supply as the top environmental concerns over issues such as air pollution, deforestation, species extinction, and global warming.
Any natural water contains dissolved chemicals, some of which are important human nutrients while others can be harmful to human health. The concentration of a water pollutant is commonly given in very small units such as parts per million (ppm) or even parts per billion (ppb). An arsenic concentration of 1 ppm means 1 part of arsenic per million parts of water. This is equivalent to one drop of arsenic in 50 liters of water. To give you a different perspective on appreciating small concentration units, converting 1 ppm to length units is 1 cm (0.4 in) in 10 km (6 miles) and converting 1 ppm to time units is 30 seconds in a year.Total dissolved solids(TDS) represent the total amount of dissolved material in water. Average TDS values for rainwater, river water, and seawater are about 4 ppm, 120 ppm, and 35,000 ppm, respectively.
Water Pollution Overview
Water pollutionis the contamination of water by an excess amount of a substance that can cause harm to human beings and/or the ecosystem. The level of water pollution depends on the abundance of the pollutant, the ecological impact of the pollutant, and the use of the water. Pollutants are derived from biological, chemical, or physical processes. Although natural processes such as volcanic eruptions or evaporation sometimes can cause water pollution, most pollution is derived from human, land-based activities (Figure 2). Water pollutants can move through different water reservoirs, as the water carrying them progresses through stages of the water cycle (Figure 3).Water residence time(the average time that a water molecule spends in a water reservoir) is very important to pollution problems because it affects pollution potential. Water in rivers has a relatively short residence time, so pollution usually is there only briefly. Of course, pollution in rivers may simply move to another reservoir, such as the ocean, where it can cause further problems. Groundwater is typically characterized by slow flow and longer residence time, which can make groundwater pollution particularly problematic. Finally,pollution residence timecan be much greater than the water residence time because a pollutant may be taken up for a long time within the ecosystem or absorbed onto sediment.
Pollutants enter water supplies frompoint sources, which are readily identifiable and relatively small locations, ornonpoint sources, which are large and more diffuse areas. Point sources of pollution include animal factory farms (Figure 4) that raise a large number and high density of livestock such as cows, pigs, and chickens. Also, pipes included are pipes from a factories or sewage treatment plants.Combined sewer systemsthat have a single set of underground pipes to collect both sewage and storm water runoff from streets for wastewater treatment can be major point sources of pollutants. During heavy rain, storm water runoff may exceed sewer capacity, causing it to back up and spilling untreated sewage directly into surface waters (Figure 5).
Nonpoint sources of pollution include agricultural fields, cities, and abandoned mines. Rainfall runs over the land and through the ground, picking up pollutants such as herbicides, pesticides, and fertilizer from agricultural fields and lawns; oil, antifreeze, animal waste, and road salt from urban areas; and acid and toxic elements from abandoned mines. Then, this pollution is carried into surface water bodies and groundwater. Nonpoint source pollution, which is the leading cause of water pollution in the U.S., is usually much more difficult and expensive to control than point source pollution because of its low concentration, multiple sources, and much greater volume of water.
Types of Water Pollutants
Oxygen-demanding wasteis an extremely important pollutant to ecosystems. Most surface water in contact with the atmosphere has a small amount of dissolved oxygen, which is needed by aquatic organisms for cellular respiration. Bacteria decompose dead organic matter and remove dissolved oxygen (O2) according to the following reaction:
organic matter+O2→CO2+H2O
Too much decaying organic matter in water is a pollutant because it removes oxygen from water, which can kill fish, shellfish, and aquatic insects. The amount of oxygen used byaerobic(in the presence of oxygen) bacterial decomposition of organic matter is calledbiochemical oxygen demand(BOD). The major source of dead organic matter in many natural waters is sewage; grass and leaves are smaller sources. An unpolluted water body with respect to BOD is a turbulent river that flows through a natural forest. Turbulence continually brings water in contact with the atmosphere where the O2content is restored. The dissolved oxygen content in such a river ranges from 10 to 14 ppm O2, BOD is low, and clean-water fish such as trout. A polluted water body with respect to oxygen is a stagnant deep lake in an urban setting with a combined sewer system. This system favors a high input of dead organic carbon from sewage overflows and limited chance for water circulation and contact with the atmosphere. In such a lake, the dissolved O2content is ≤5 ppm O2, BOD is high, and low O2-tolerant fish, such as carp and catfish dominate.
Excessive plant nutrients, particularly nitrogen (N) and phosphorous (P), are pollutants closely related to oxygen-demanding waste. Aquatic plants require about 15 nutrients for growth, most of which are plentiful in water. N and P are calledlimiting nutrients, however, because they usually are present in water at low concentrations and therefore restrict the total amount of plant growth. This explains why N and P are major ingredients in most fertilizer. High concentrations of N and P from human sources (mostly agricultural and urban runoff including fertilizer, sewage, and phosphorus-based detergent) can causeculturaleutrophication, which leads to the rapid growth of aquatic producers, particularly algae. Thick mats of floating algae or rooted plants lead to a form of water pollution that damages the ecosystem by clogging fish gills and blocking sunlight. A small percentage of algal species produce toxins that can kill animals, including humans. Exponential growths of these algae are calledharmful algal blooms.When the prolific algal layer dies, it becomes oxygen-demanding waste, which can create very low O2concentrations in thewater (< 2 ppm O2), a condition calledhypoxia.This results inadead zonebecause it causes death from asphyxiation to organisms that are unable to leave that environment. An estimated 50% of lakes in North America, Europe, and Asia are negatively impacted by cultural eutrophication. In addition, the size and number of marine hypoxic zones have grown dramatically over the past 50 years including a very large dead zone located offshore Louisiana in the Gulf of Mexico. Cultural eutrophication and hypoxia are difficult to combat, because they are caused primarily by nonpoint source pollution, which is difficult to regulate, and N and P, which are difficult to remove from wastewater.
Pathogensare disease-causing microorganisms, e.g., viruses, bacteria, parasitic worms, and protozoa, which cause a variety of intestinal diseases such as dysentery, typhoid fever, and cholera. Pathogens are the major cause of the water pollution crisis discussed at the beginning of this section. Unfortunately nearly a billion people around the world are exposed to waterborne pathogen pollution daily and around 1.5 million children mainly in underdeveloped countries die every year of waterborne diseases from pathogens.Pathogens enter water primarily from human and animal fecal waste due to inadequate sewage treatment. In many underdeveloped countries, sewage is discharged into local waters either untreated or after only rudimentary treatment. In developed countries untreated sewage discharge can occur from overflows of combined sewer systems, poorly managed livestock factory farms, and leaky or broken sewage collection systems.Water with pathogens can be remediated by adding chlorine or ozone, by boiling, or by treating the sewage in the first place.
Oil spillsare another kind of organic pollution. Oil spills can result from supertanker accidents such as the Exxon Valdez in 1989, which spilled 10 million gallons of oil into the rich ecosystem of coastal Alaska and killed massive numbers of animals. The largest marine oil spill was the Deepwater Horizon disaster, which began with a natural gas explosion (Figure 6) at an oil well 65 km offshore of Louisiana and flowed for 3 months in 2010, releasing an estimated 200 million gallons of oil. The worst oil spill ever occurred during the Persian Gulf war of 1991, when Iraq deliberately dumped approximately 200 million gallons of oil in offshore Kuwait and set more than 700 oil well fires that released enormous clouds of smoke and acid rain for over nine months.
During an oil spill on water, oil floats to the surface because it is less dense than water, and the lightest hydrocarbons evaporate, decreasing the size of the spill but polluting the air. Then, bacteria begin to decompose the remaining oil, in a process that can take many years. After several months only about 15% of the original volume may remain, but it is in thick asphalt lumps, a form that is particularly harmful to birds, fish, and shellfish. Cleanup operations can includeskimmer shipsthat vacuum oil from the water surface (effective only for small spills), controlledburning(works only in early stages before the light, ignitable part evaporates but also pollutes the air),dispersants(detergents that break up oil to accelerate its decomposition, but some dispersants may be toxic to the ecosystem), andbioremediation(adding microorganisms that specialize in quickly decomposing oil, but this can disrupt the natural ecosystem).
Toxic chemicalsinvolve many different kinds and sources, primarily from industry and mining. General kinds of toxic chemicals includehazardous chemicals andpersistent organic pollutantsthat include DDT(pesticide),dioxin(herbicide by-product), andPCBs(polychlorinated biphenyls, which were used as a liquid insulator in electric transformers).Persistent organic pollutants(POPs) are long-lived in the environment, biomagnify through the food chain, and can be toxic. Another category of toxic chemicals includesradioactive materialssuch as cesium, iodine, uranium, and radon gas, which can result in long-term exposure to radioactivity if it gets into the body. A final group of toxic chemicals isheavy metalssuch as lead, mercury, arsenic, cadmium, and chromium, which can accumulate through the food chain. Heavy metals are commonly produced by industry and at metallic ore mines. Arsenic and mercury are discussed in more detail below.
Arsenic(As) has been famous as an agent of death for many centuries. Only recently have scientists recognized that health problems can be caused by drinking small arsenic concentrations in water over a long time. It enters the water supply naturally from weathering of arsenic-rich minerals and from human activities such as coal burning and smelting of metallic ores. The worst case of arsenic poisoning occurred in the densely populated impoverished country of Bangladesh, which had experienced 100,000s of deaths from diarrhea and cholera each year from drinking surface water contaminated with pathogens due to improper sewage treatment. In the 1970s the United Nations provided aid for millions of shallow water wells, which resulted in a dramatic drop in pathogenic diseases. Unfortunately, many of the wells produced water naturally rich in arsenic. Tragically, there are an estimated 77 million people (about half of the population) who inadvertently may have been exposed to toxic levels of arsenic in Bangladesh as a result. The World Health Organization has called it the largest mass poisoning of a population in history.
Mercury(Hg) is used in a variety of electrical products, such as dry cell batteries, fluorescent light bulbs, and switches, as well as in the manufacture of paint, paper, vinyl chloride, and fungicides. Mercury acts on the central nervous system and can cause loss of sight, feeling, and hearing as well as nervousness, shakiness, and death. Like arsenic, mercury enters the water supply naturally from weathering of mercury-rich minerals and from human activities such as coal burning and metal processing. A famous mercury poisoning case in Minamata, Japan involved methylmercury-rich industrial discharge that caused high Hg levels in fish. People in the local fishing villages ate fish up to three times per day for over 30 years, which resulted in over 2,000 deaths. During that time the responsible company and national government did little to mitigate, help alleviate, or even acknowledge the problem.
Hard watercontains abundant calcium and magnesium, which reduces its ability to develop soapsuds and enhancesscale(calcium and magnesium carbonate minerals) formation on hot water equipment. Water softeners remove calcium and magnesium, which allows the water to lather easily and resist scale formation. Hard water develops naturally from the dissolution of calcium and magnesium carbonate minerals in soil; it does not have negative health effects in people.
Groundwater pollutioncan occur from underground sources and all of the pollution sources that contaminate surface waters. Common sources of groundwater pollution are leaking underground storage tanks for fuel, septic tanks, agricultural activity, landfills, and fossil fuel extraction. Common groundwater pollutants include nitrate, pesticides, volatile organic compounds, and petroleum products. Another troublesome feature of groundwater pollution is that small amounts of certain pollutants, e.g., petroleum products and organic solvents, can contaminate large areas. In Denver, Colorado 80 liters of several organic solvents contaminated 4.5 trillion liters of groundwater and produced a 5 km long contaminant plume. A major threat to groundwater quality is fromunderground fuel storage tanks. Fuel tanks commonly are stored underground at gas stations to reduce explosion hazards. Before 1988 in the U.S. these storage tanks could be made of metal, which can corrode, leak, and quickly contaminate local groundwater. Now, leak detectors are required and the metal storage tanks are supposed to be protected from corrosion or replaced with fiberglass tanks. Currently there are around 600,000 underground fuel storage tanks in the U.S. and over 30% still do not comply with EPA regulations regarding either release prevention or leak detection.
Resolution of the global water pollution crisis requires multiple approaches to improve the quality of our fresh water and move towards sustainability. The most deadly form of water pollution, pathogenic microorganisms that cause waterborne diseases, kills almost 2 million people in underdeveloped countries every year. The best strategy for addressing this problem is proper sewage (wastewater) treatment. Untreated sewage is not only a major cause of pathogenic diseases, but also a major source of other pollutants, including oxygen-demanding waste, nutrients (N and P, particularly), and toxic heavy metals. Wastewater treatment is done at asewage treatment plantin urban areas and through aseptic tank systemin rural areas.
The main purpose ofsewage (wastewater) treatmentis to remove organic matter (oxygen-demanding waste) and kill bacteria. Special methods also can be used to remove nutrients and other pollutants. The numerous steps at a conventional sewage treatment plant includepretreatment(screening and removal of sand and gravel),primary treatment(settling or floatation to remove organic solids, fat, and grease),secondary treatment(aerobic bacterial decomposition of organic solids),tertiary treatment(bacterial decomposition of nutrients and filtration),disinfection(treatment with chlorine, ozone, ultraviolet light, or bleach to kill most microbes), and eitherdischargeto surface waters (usually a local river) orreusefor some other purpose, such as irrigation, habitat preservation, and artificial groundwater recharge (Figure 1).
The concentrated organic solid produced during primary and secondary treatment is calledsludge, which is treated in a variety of ways including landfill disposal, incineration, use as fertilizer, and anaerobic bacterial decomposition, which is done in the absence of oxygen. Anaerobic decomposition of sludge produces methane gas, which can be used as an energy source. To reduce water pollution problems, separate sewer systems (where street runoff goes to rivers and only wastewater goes to a wastewater treatment plant) are much better than combined sewer systems, which can overflow and release untreated sewage into surface waters during heavy rain. Some cities such as Chicago, Illinois have constructed large underground caverns and also use abandoned rock quarries to hold storm sewer overflow. After the rain stops, the stored water goes to the sewage treatment plant for processing.
Aseptic tanksystemis an individual sewage treatment system for homes in typically rural settings. The basic components of a septic tank system (Figure 2) include a sewer line from the house, aseptic tank(a large container where sludge settles to the bottom and microorganisms decompose the organic solids anaerobically), and the drain field (network of perforated pipes where the clarified water seeps into the soil and is further purified by bacteria). Water pollution problems occur if the septic tank malfunctions, which usually occurs when a system is established in the wrong type of soil or maintained poorly.
For many developing countries, financial aid is necessary to build adequate sewage treatment facilities. The World Health Organization estimates an estimated cost savings of between $3 and $34 for every $1 invested in clean water delivery and sanitation.The cost savings are from health care savings, gains in work and school productivity, and prevented deaths. Simple and inexpensive techniques for treating water at home include chlorination, filters, and solar disinfection. Another alternative is to useconstructed wetlandstechnology (marshes built to treat contaminated water), which is simpler and cheaper than a conventional sewage treatment plant.
Bottled waterisnota sustainable solution to the water crisis. Bottled water is not necessarily any safer than the U.S. public water supply, it costs on average about 700 times more than U.S. tap water, and every year it uses approximately 200 billion plastic and glass bottles that have a relatively low rate of recycling. Compared to tap water, it uses much more energy, mainly in bottle manufacturing and long-distance transportation. If you don’t like the taste of your tap water, then please use a water filter instead of bottled water!
CLEAN WATER ACT
During the early 1900s rapid industrialization in the U.S. resulted in widespread water pollution due to free discharge of waste into surface waters. The Cuyahoga River in northeast Ohio caught fire numerous times, including a famous fire in 1969 that caught the nation’s attention. In 1972 Congress passed one of the most important environmental laws in U.S. history, the Federal Water Pollution Control Act, which is more commonly called theClean Water Act. The purpose of the Clean Water Act and later amendments is to maintain and restore water quality, or in simpler terms to make our water swimmable and fishable. It became illegal to dump pollution into surface water unless there was formal permission and U.S. water quality improved significantly as a result. More progress is needed because currently the EPA considers over 40,000 U.S. water bodies as impaired, most commonly due to pathogens, metals, plant nutrients, and oxygen depletion. Another concern is protecting groundwater quality, which is not yet addressed sufficiently by federal law.
