8.4.3 Water ResourcesWater is one of our most precious resources. Our bodies are 2/3 made of water. We not only need water to drink, but water is a major part of all the food we eat. But our need for water goes far beyond that. We use water in our homes, at work, and even to generate our electricity. Not everyone has adequate access to clean water, however, and in many parts of the world water resources are becoming scarce.

How Do People Use Water Resources?How much water do you use in a day? The amount turns out to be a lot more than you might think. There is water that you personally use each day. But there is also water needed to grow and raise your food (and water in the food!). Water is also used to make your clothes, your house, and most everything in it. In addition, water is needed to create and run your towns and cities. When you put it all together, people use a lot of water.

Home Use Take a look at the chart showing home uses of water [showing average water use for a shower, bath, washing your hands, flushing toilet, etc. – such as: http://ciese.org/k12partner01/PersonalWaterUseChart.html]. Think about an average day for you. Add up all of the different amounts of water you use. Do you get a number that is above or below average? The average American uses 98 gallons (371 liters) of water per day. The need is different in different parts of the country depending upon factors such as climate. The average in Nevada is 190 gallons of water per person per day. In Maine, it is only 54.

Look at the pie chart in Figure 1 [top figure at http://www.epa.gov/watersense/our_water/water_use_today.html]. Flushing toilets is the single most water consuming activity Americans do in their homes. However, we even use water without knowing it. An average American home will waste more than 10,000 gallons of water each year from dripping faucets, running toilets, and other leaks (14% of our total home use). This is more than a trillion wasted gallons of water in the U.S. each year.

Water for Food We use water in other ways as well. The vegetables you eat are mostly water, but they take even more water to grow over a periods of months. Making a single pound of rice can take 250-600 gallons of water. Meat takes a lot of water, because animals like cows drink a lot of water over their lifetime. It can take 3000 gallons of water to end up with a quarter-pound hamburger patty. Next time you eat a hamburger, try to imagine also consuming 3000 gallons of water. Water is needed for many agricultural processes other than growing food. Water is needed to grow cotton to make clothes, raise sheep to make wool, and grow trees to make paper for books and wood for houses.

Industrial factory processes use a great amount of water. Water is used to wash, clean, dissolve, and create many materials. Chemical reactions used to make materials such as plastics require a great amount of water. Water is also used to cool down machinery so that it doesn’t get too hot.

Water for Power As was already discussed earlier in this unit, hydroelectric power is one of the leading forms of renewable energy. Dams placed across rivers create a vertical drop that can be used to convert gravitational potential energy into electricity. When water falls down through turbines within the dam, the spinning turbines create energy. Hydroelectric power plants generate 16% of the world’s electricity.

However, water is used for making electricity in another, even greater way. Many power plants burn a fuel such as coal or natural gas to turn water into steam to run a steam turbine. That steam has to be cooled down so that it can be heated again. The cooling process requires a great amount of additional water. As Figure 2 [bottom figure at http://www.epa.gov/watersense/our_water/water_use_today.html] shows, it is the largest single end use of water. However, that water is usually returned back into ponds or rivers, so it different than the use of water for agriculture because it can be reused again. But, when you turn on a light in your home or school, you are also using water.

When you add it all together, for all the different applications, people use a lot of water. The world’s population now uses more than 9 trillion cubic meters of water per year. That is as much as a cube of water 21 kilometers on a side. Americans use the most: over 2800 cubic meters per person, or over 2050 gallons per person per day.

[Figures: Table of personal water use (http://ciese.org/k12partner01/PersonalWaterUseChart.html); pie chart of home water use (http://www.epa.gov/watersense/our_water/water_use_today.html); ?graphic equating one hamburger patty with 6000 gallons of water; pie chart of total water use (http://www.epa.gov/watersense/our_water/water_use_today.html);

(this is actually a 6000 gallon tank!)

How Do People Obtain Surface Water?Most of the world’s people get their water from surface water, mostly in the form of rivers and lakes. In the US, 80% of total water resources comes from surface water (the rest from groundwater). This may seem strange if you remember that rivers and lakes make up a tiny percentage of freshwater. However, it turns out that a lot of water moves quickly through streams and lakes, even if there isn’t a lot there at any given point in time.

Fresh Water Most of Earth’s accessible water is salt water (96.5%), and most is in the ocean. While there are mammals such as whales, dolphins, and seals that have adapted to drinking seawater, we are not one of them. We can use salt water for some of our needs, such as cooling electric power plants, but not for most uses. So, we have to look to the remaining 3.5% of Earth’s water, which is fresh water. Of this, 70% is in the form of ice, mostly as the giant ice sheets of Antarctica and Greenland. As these are far away from most people, they are not useful supplies for water resources. Nearly all of what is left over, the other 30%, is below the land surface as groundwater. Everything else is less than 1%. Lakes contain 0.26% and all rivers are only 0.006% of freshwater.

Residence Time However, there is another factor that is important in understanding the availability of water resources, and that is how quickly the resource gets replenished. If you pump out groundwater, it can take a long time to replenish the supply. However, it is continually raining, at least in some parts of the world, so rivers keep flowing. You can pump water out of a river, and more will usually quickly come to take its place. On average, a molecule of water will stay in the ocean for thousands of years. It can stay as groundwater for tens of thousands of years. But the average time a molecule of water stays in a river is only a couple months.

There are limits, however. Rainfall is naturally higher in some parts than others. For example, rainfall is high in the Pacific Northwest region of states such as Oregon and Washington. Rainfall is usually much lower in the Southwestern states of Arizona, Nevada, and New Mexico. However, human consumption of water and changing regional climates have recently caused many rivers to get critically low. In some cases, there is actually no water left by the time the river reaches the ocean. The Southwestern U.S. has been experiencing an extended drought for the past several decades, and many rivers there are running critically low.

Dams and Reservoirs Another concern with the use of surface fresh water is that rivers don’t always run at the same level all year. This is especially true in countries like India that have a monsoon climate, where it may rain heavily for one part of the year but not rain at all for other parts of the year. Even in US, it tends to rain more in the spring than in the late summer and fall. In addition, any part of the country can occasionally suffer from droughts, where rainfall is far below normal for months or even years. In order to help balance out this variability, dams and reservoirs can be built. A dam is placed along a river to store large amounts of river water. Many dams are built to supply hydroelectric power. They can also accumulate and store water during rainy times for use during drier times.

Some reservoirs are special human-made lakes that are built just for the purpose of storing water. The water supply for New York City is maintained through the use of a network of human-made reservoirs that can hold up to 550 billion gallons of water. There are concerns that arise with the use of dams and reservoirs, however. They can block the flow of fish in a river. Over time they can fill up with sediment. The greater surface area of the water causes more water to be lost to evaporation. The standing water can even lead to an increase in mosquitos and mosquito-borne diseases.

Supplying Water The engineering challenges of supplying continuous water to hundreds of millions of Americans are enormous. A huge underground network of pipes is required to get fresh water to homes and businesses and then to get wastewater away from them. Wherever possible, gravity is used to help. Water intakes from rivers and lakes are usually taken uphill from towns and cities so that the water will run downhill on its own to where it is needed. If there are valleys in between, then aqueducts are needed to carry the water across. If the land is too flat, or if the source is downhill, then massive pumps are needed to pump water uphill, where it is usually stored in large water towers.

Recreation A very important use of water is for recreation. Many people vacation at places where there is water: streams, lakes, and the ocean. People enjoy swimming, boating, surfing, water skiing, snorkeling, scuba diving, fishing, or just relaxing by the beach. Many sports that students and adults participate in involve water, such as swimming, water polo, and boating. Water has many practical uses

for the day-to-day operation of industry and society, but one of the most important uses is simply as a beautiful and enjoyable place for people to visit.

[Figures: Graphic to demonstrate the amounts of water in rivers and lakes compared to groundwater and glaciers; photo of the water intake in a river; photo of a reservoir; photo of a water tower; photo of Roman aqueduct; photo of people at a beach]

(this is actually an intake house for St. Louis, upstream on the Mississippi by the Chain of Rocks bridge)

How Do People Use Groundwater?Suppose you live far from a river or lake. How could you get water for your needs? You might be in luck. The water table in your area might be only a few meters

underground. In fact, in some places called springs the water table actually meets the surface (other than in cases of streams or lakes, which are also cases where the water table meets the surface). Springs form where groundwater flows out of the rock at the surface.

Currently, about 20% of American water use comes from groundwater, but that number is rising. It already supplies a third of US drinking water, 40% of water for growing crops, and 60% of water used for raising livestock.

Aquifers Any underground layer of permeable rock or sediment that holds water and allows it to flow is called an aquifer. Aquifers can range in size from a small patch to an area the size of several states. The huge Ogallala aquifer lies beneath the plains of the Midwest US, from South Dakota to Texas. This aquifer provides water for millions of people, as well as for crops and livestock.

Aquifers are not unlimited sources of water. If people take water from an aquifer faster than the aquifer refills, then the level of the water table in the aquifer will drop. This makes it more difficult to reach the water, and wells could eventually run dry. This is currently happening to many aquifers in the U.S. and around the world.

Movement in Aquifers Do you picture groundwater as a large, still pool beneath Earth’s surface? In fact, if you were down there, you might not even notice it. Groundwater seeps through solid layers of rock or soil. The rate of motion depends upon the slope of the water table and the permeability of the rocks. Some groundwater moves only a few centimeters a day. At that rate, the water moves about 10 meters a year. Groundwater may travel many hundreds of kilometers and stay in an aquifer for many thousands of years before coming to the surface again.

Wells Since ancient times, people have brought groundwater to the surface for drinking and other everyday uses. People can obtain groundwater from an aquifer by drilling a well below the water table. When the bottom of the well is in a saturated zone, the well contains water. If the water table drops below the bottom of the well, however, the well will run dry and water cannot be obtained from it.

Using Pumps Long ago, people dug wells by hand. Thy used a bucket to bring up the water. People may also have used simple pumps. Today, however, most wells are dug with well-drilling equipment. Mechanical pumps bring up the groundwater.

Pumping water out of an aquifer may lower the water level in the area around the well. If too much water is pumped out too fast, a well may run dry. The owners of the well will have to either wait until the local water table rises (from rainfall or horizontal groundwater flow) or drill deeper to reach the lowered water table.

Relying on Pressure Another option for bringing up groundwater is an artesian well. In an artesian well (ahr TEE zhun), water rises on its own because of pressure within the aquifer.

In some aquifers, groundwater becomes trapped between two layers of impermeable rock or sediment. This water is under great pressure from the water extending back up the aquifer. If the top layer of impermeable rock is punctured, the pressure sends the water spurting up through the hole. No pump is necessary – in an artesian well, water pressure does the job.

Oases Have you ever wondered how an oasis in a desert forms? An oasis is an isolated region of vegetation in a desert where groundwater comes to the surface from an aquifer underneath. In some cases, the aquifer bends so that it is in contact with the surface. In other cases a fault in the rock provides a natural artesian well, with pressure within the aquifer pushing water up along the fault to the surface.

<Figures: Map of Ogallala aquifer (perhaps both showing thickness and changes) ; graphic showing a cone of depression in the water table around a water well; photo of modern water well pump jack; photo of desert oasis; show artwork of two kinds of oases and an artesian well..>

[Did you know?: Deep underground, water in some areas, usually near volcanoes, experiences great heat and pressure. The pressure forces boiling-hot water to the surface, creating bubbling hot springs, erupting geysers, and jets of steam. More than half of the known geysers in the world are found in Yellowstone National Park.<Use Figure in top left of p. 22, IS-Water&Atmosphere>]

How Do People Use Ocean Water?Most of Earth’s available water is in the ocean, and even though it is salt water, it is still a valuable human resource. The ocean supports a vast and diverse part of the biosphere, which provides much of the food humans eat. In addition, technology is finding ways to remove the salt from salt water to make it drinkable by humans.

Harvesting Sea Life What sea life do you think you use? You can probably list the names of many types of fish that you eat. Worldwide, the greatest volumes of fish caught and eaten are of anchovies, pollock, mackerel, herring, and tuna. Other common fish eaten include salmon, cod, and eel. People also eat many other types of sea animal such as crustaceans (shrimp, crabs, and lobsters) and molluscs (clams, mussels, oysters, scallops, squid, and octopus). About 1 billion people rely on fish as their main source of animal protein. Most of these people are in developing countries in Asia. Fish provide about 7% of animal protein for people in North and Central America, but over 25% for people in Asia.

Nearly all fish are harvested from coastal waters. This is not because these waters are close to shore and therefore easy to get to. It is because these are where nutrients in the water support large populations of single-celled organisms called plankton on which the fish feed. Some of the nutrients are washed off of the land

and enter the ocean from rivers. In some cases nutrients are brought up to the surface by a process called upwelling. In upwelling, wind and ocean currents interact with the outlines of the continent in such a way that warm surface water is pushed away from land and cold deep water is pulled up to take its place. This supports populations of plankton and fish because the upwelling water carries nutrients to the surface, replacing the nutrients that have been eaten by the plankton.

Fisheries Fisheries are areas where fish are harvested. If used wisely, fisheries naturally renew themselves each year. New fish hatch, replacing those that are caught, but only as long as the fishery is not overfished. Better technology has allowed people to quickly catch large numbers of fish. The fish can be caught faster than they can reproduce. When fish reproduction decreases, there are fewer fish each season. Eventually, the fish in the fishery may become very scarce. Some species of fish have been overfished, and it may take many years before their populations are large enough to be fished again.

Aquaculture One way to ensure a continuous supply of food that does not significantly affect wild fish populations is to carry out aquaculture. Aquaculture is the farming of saltwater and freshwater organisms by creating an environment for the organisms to live in. To help the organisms thrive, nutrient levels, water temperature, light, and other factors must be controlled. Oysters, abalone, and shrimp have been successfully farmed in artificial ponds and protected bays. Even landlocked regions can produce seafood using aquaculture. For example, salmon are now being raised in Nebraska fields that once were cattle ranches. About 25% of the wild fish harvest that is caught is now used to make fish food and oils used for aquaculture.

Algae People don’t just eat sea animals, however. Almost 10 million tons of algae are harvested from the ocean each year. This is largely in the form of multi-cellular algae called seaweed. The seaweed can be eaten directly or processed into a gelatin-like base for many other foods such as ice cream, salad dressing, and jelly. The processed seaweed is also used to make many other common household products such as detergents, shampoos, toothpaste, cosmetics, and paints. In addition, ocean algae can even be used to make biofuels that may one day be used to power cars and planes.

Desalination It turns out that there is a way for people to drink ocean water. The salt can be removed from the water by processes called desalination. This has been done for many years in places where no fresh water is available, such as on boats or submarines. Many countries are now doing this to supply drinking water for their people. The most common way to desalinate salt water is to boil it (see Figure XX). The water that boils off at the surface does not contain any salt, so if the water vapor is captured and allowed to condense back into liquid water, fresh water can be collected.

Desalination takes more energy than most other means of obtaining water, so it costs more. Most American homes currently pay about $2-5 for 1000 gallons of water. This is about the same as the cost of desalinating 1000 gallons water. So at current prices, the cost of delivering desalinated water could double the price. (For comparison, the same amount of water purchased in plastic bottles would cost about $8000.) However, as costs of solar-based energy becomes cheaper and costs of water increase, many parts of the world are turning to desalination for their water. One concern with desalination is what to do with all of the salt that is left over. Salt is toxic to most life, so it needs to be disposed of carefully.

<Figures: photo of fishing, such as on p.160; photo of seaweeds; ocean upwelling diagram (p.165); desalination diagram (p.163)>

How Can People Conserve Water?Most American’s take water for granted. In most places of the US we can turn on a faucet and clean water will always flow out of it. There are many parts of the world, however, where this is not the case. According to the United Nations, more than 1.2 billion people (about 4 times the total population of the US) do not have access to clean drinking water. In addition, about 2.8 billion people suffer from insufficient water supplies at least one month out of every year, during a dry season. As human populations increase, more and more areas, including those in the US, are running out of available water. Because of this, tremendous efforts are now being made to conserve water.

US Water Distribution Water resources are not distributed evenly throughout the US. Look at the accompanying map of precipitation amounts [like http://www.climatesource.com/images/ppt_ann.gif]. Which states do you see are the wettest? Which states are the driest? The average precipitation for the US is about 70 cm per year. Is your state above or below this? In general, the Southeastern US gets very high average rainfall, though the very highest are in western Oregon and Washington. The western states, particularly the southwestern states, get the least amount of rainfall. In addition, many climate projections suggest that these areas might get even less water in the future. These states are more susceptible to droughts and water shortages.

Reduce, Reuse, Recycle There are several ways to deal with the shortage of a resource such as water. One way is to try to get more of it. Another way is to conserve it. In the case of water, it is sometimes possible to get more water for a region, but it is costly and difficult. In certain cases, the atmosphere can be “seeded” with tiny dust particles that can help to start rainfall. As we just saw, ocean water can be desalinated, and it could be pumped great distances uphill from coasts. However, these solutions are usually too expensive to be practical. We also saw how some areas can get water from the ground, but groundwater refills very slowly and will run out at some point.

The best way to reduce water shortages is by conserving water: by reducing, reusing, and recycling. In many places it is customary to reuse water. For example, water used for washing or cleaning (called graywater) would no longer be drinkable but could be used outside in a garden or collected in a bucket in the shower to be used in flushing toilets. Rainfall on your roof can be collected in rain barrels at the end of the drains. In some places, water is even entirely recycled. After going through waste recycling plants, water is sometimes so well cleaned and purified that it is available for drinking again.

Home Water Use The easiest way to cut back on water shortages, however, is to use less water. This can be done at all levels; from personal water use in the home to changes in water use for agriculture, industry, and power generation. Look back at the chart in Figure XXX of all the different ways that people use water in their homes. Can you think of ways that you could use less water for each of these? For example, make sure that clothes washing machines and dishwashers are full before you run them. Take shorter showers or turn off the shower while you are soaping up. Choose plants for your lawn or garden that need less water. Turn off the faucet while you are brushing your teeth. Low-flow showerheads or faucets use less water. If you look carefully, you could probably find ways to reduce your water use by at least 50%.

Large-Scale Projects Many water-conserving practices are being done on a large scale. Regulations require new toilets to use much less water than old ones,

resulting in a significant reduction in national water use (remember that flushing toilets is the single largest home use of water). Car washes recycle their water, and there are now even waterless car washes.

Agriculture Huge reductions in water use are also being gained by improving agricultural practices. Older practices of either flooding fields or spraying water lost large amounts of water to evaporation. Modern watering methods use drip irrigation, where water is applied to plant roots with minimal losses [Show figure such as http://growerssupply.files.wordpress.com/2012/07/drip-irrigation-system-110400_16-crop.jpg].

Energy Changes in national energy sources are also having an effect. Renewable energy sources such as photovoltaic solar panels or wind turbines do not use any water to generate electricity (unlike coal, nuclear, or natural gas-powered plants) so as more renewable energy is used, less water will be used. It also takes a lot of energy to clean and deliver water to you, and not just for complex technologies like desalination. Letting your faucet run for about 5 minutes takes about as much energy as leaving a 60-watt light bulb run all day. So there is a positive feedback here: using less water will require less energy, which will use less water. Human needs for water and energy are both increasing, but the two resources are closely linked together.

[Figures: Map of US precipitation (like http://www.climatesource.com/images/ppt_ann.gif); photo of home rain barrel; photo of drip irrigation (like http://growerssupply.files.wordpress.com/2012/07/drip-irrigation-system-110400_16-crop.jpg)]

Assessment1. a. Evaluate Suppose you are water manager for a town in southern

California. There has been a drought and river and reservoir levels are critically low. Evaluate other options for obtaining water. What would you choose and why?b. Explain Why does it make more sense to build a reservoir uphill from a town than downhill from it?c. CCC (Cause and Effect) Why could it save water if trends changed and most everyone had short hair?

2. a. Engaging in Argument Construct and defend an argument for why a vegetarian diet is better than eating meat in terms of conserving water.b. CCC (Connections to Engineering and Technology) Suppose that more and more of US water comes from desalination. Devise a plan for what to do with all of the leftover salt.

Study Guide8.3.4 Water ResourcesHow Do People Use Water Resources? People use water in their homes and businesses, and water is used in industry, agriculture, and electricity generation.How Do People Obtain Surface Water? Surface water is taken from rivers and lakes and carried to its many uses through networks of pipes and aqueducts.How Do People Obtain Groundwater? Groundwater is pumped out of the ground from aquifers using wells.How Do People Use Ocean Water? Ocean water can desalinated for human use, but also provides many important resources such as fish and seaweed.How Can People Conserve Water? People can conserve water by reducing the amount they use through improved technologies and better awareness, as well as by reusing and recycling water.

Some sources:http://www.scientificamerican.com/article/graphic-science-how-much-water-nations-consume/http://www.pnas.org/content/109/9/3232http://water.usgs.gov/edu/wateruse/pdf/wudomestic-2005.pdfhttp://www.waterfootprint.org/Reports/Report50-NationalWaterFootprints-Vol1.pdfhttp://water.usgs.gov/edu/wugw.html