The Water Cycle

Educator's Notes

The fresh water resources of the Atlantic Provinces are related to the larger water resources of the oceans and the atmosphere, which go well beyond our provincial or national boundaries. The total amount of water in the world is estimated at over a billion cubic kilometres. While its forms may change from oceans to clouds, to precipitation, to rivers, to ice fields, and so on, the total quantity of water has remained constant for the past 3 to 5 million years. A closer look reveals that only 2.5% of the world's water is fresh. Most of this is locked into glaciers and polar ice caps. Of the remainder, 30.9% is underground and 0.4% is above ground as rivers, lakes and water vapour. This means that only one hundredth of one percent of the Earth's total water serves human-kind's fresh water needs.

This comparatively small amount of water, which is essential to life on land, is constantly being exchanged between the Earth and the atmosphere. The endless circulation of water from the atmosphere to the Earth and its return to the atmosphere through condensation, precipitation, evaporation and transpiration is called the hydrologic cycle.

The Hydrologic Cycle

All of the water on Earth continually cycles through a process which sees water changing its location or physical state through thermal reactions. In accordance with the law of conservation of matter, water is not created or destroyed in this process; it simply changes form. Water can be found in all three states of matter during the hydrologic cycle: solid (in the form of ice), liquid (in fluid water) and gaseous (in the form of water vapour). Hydrology is the study of the movement and distribution of the waters of the earth.

The hydrologic cycle (or water cycle, as it is commonly known) as it operates in the Atlantic region, generates a high annual precipitation. Rivers, lakes and groundwater reserves are continually being replenished, although the process varies with local geology. In Newfoundland and Labrador, predominantly rocky land surfaces often mean a quick runoff after a rain or snow melt. Just the opposite is true in Prince Edward Island, where a great deal of precipitation (about 20%) infiltrates the porous soil cover¹. Nova Scotia and New Brunswick have land areas which demonstrate both extremes.

The heating of ocean water by the sun is the key process that keeps the hydrologic cycle in motion. As liquid water is heated, its surface molecules become sufficiently energized to break free of the attractive force binding them together, and evaporation takes place. 97% of all water vapour comes from the world's oceans which serve as massive storage tanks in the hydrologic cycle.

Water can also evaporate from ground moisture, rivers, and lakes, directly from snow and ice (sublimation) and even from rain drops as they fall to the ground. Plants also give off vapour through their leaves (transpiration). A large oak tree, for example, can give off more than 136 000 litres of transpired water in a year. As much as 40% of Canadian water is evaporated or transpired.²

As water vapour rises higher in the atmosphere, it cools until it condenses into a liquid form once more. Such vapour often condenses around tiny particles of dust floating through the air. When enough water droplets combine together, they form a cloud. As the air continues to cool, the cloud becomes saturated with water droplets and it begins to rain. When water returns to the surface of the Earth in the form of rain, snow, sleet or hail, it is called precipitation.

Some precipitation is intercepted by plants, but most falls to the Earth's surface and begins to move toward the ocean through the established carrier system of streams, lakes and rivers. Some will infiltrate the Earth to become groundwater. Even within the ground, water continues to flow. It can percolate through cracks and pores in soil and rocks down to the water table below; it can move back up to the surface by capillary action; or it can move horizontally under the Earth's surface until it re-enters a surface water system.

The basic pattern of the hydrologic cycle seems very simple: Evaporation - Condensation - Infiltration - Runoff. But the cycle is not as smooth or regular as it first may seem. There are often seasons when one aspect of the cycle may dominate. Although the cycle balances what goes up with what comes down, one phase of the cycle is "frozen" in the colder regions during the winter season. During the Canadian winter, for example, most of the precipitation is simply stored as snow or ice on the ground. Later, during the spring melt, huge quantities of water are released quickly, which results in heavy spring runoff and (potentially) flooding. Alternatively, in the summer, extensive evaporation and transpiration during long hot spells may decrease stream levels.

The sun's heat or solar energy draws water into the atmosphere through evaporation, and it is the Earth's gravity that returns the water to the Earth's surface as precipitation. The majority of fresh water use takes place in the surface and groundwater stages of the hydrologic cycle.

It is hard to believe that there could ever be a serious water shortage problem in Nova Scotia. Our total annual precipitation is fairly high – approximately 1 200 to 1 400 millimetres compared to between 750 and 950 millimetres in central Ontario or between 250 and 400 millimetres in southern Saskatchewan. Flying over our province, you see countless lakes, rivers and streams.

The problem with Nova Scotia's water resources (freshwater) is that while there is a great deal of water available in the province, most of it cannot be used for drinking water supply without extensive treatment.

The Ocean³

In a way, we are the ocean and the ocean is us. Life probably began in the ocean and thrived there for more than three billion years before some proto-amphibian gathered up its courage and slopped onto the dirt! All of us – humans, wombats and redwoods – still carry an ocean inside. Our blood, eggs, the fluid behind the corneas of our eyes and the insides of our cells are salt water. Just as about three-quarters of the Earth's surface is salt water, about three-quarters of each of us is salt water.

The ocean has a profound effect on our planet and on ourselves. It moderates and affects weather. The majority of the Earth's oxygen is generated by ocean plants, and most of the Earth's reservoir of carbon dioxide (a gas critical to plant survival and the control of climate) is dissolved in the ocean. The ocean provides us with an immense amount of food and other natural resources, and 90% of the world's trade is transported on its waves. If it weren't for the ocean, there probably would be no life on Earth.

How Big is the Ocean and What's it Really Like?

The Earth is a water planet. The ocean covers 71% of its surface (61% of the Northern Hemisphere and 81% of the Southern Hemisphere). We use the term "ocean" because it is a single entity. Traditionally, we have divided the waters into "oceans"; the Pacific, Atlantic and Indian; and "seas"; the Mediterranean, Caribbean and Baltic; using various land masses as boundaries. In reality, these terms are just for our convenience – all of these water masses are interconnected and water flows freely throughout. As far as its chemical makeup is concerned, cups of seawater taken from all parts of the world are almost identical. Because it's all from the world ocean.

The ocean covers 360 million square kilometres and its average depth is about 3 800 metres. By comparison, the average height of the land is 845 metres. And it's cold, too. The average ocean temperature is 3.9°C Why so cold? Because most of the ocean is deep and, even in the tropics, deep water is cold water.

How deep is the ocean and where is the deepest spot in the ocean? The deepest spot is the Challenger Deep, and additional divot in the cavernous Mariana Trench, located just east of Guam. The ocean floor at this spot is 11 022 metres from the surface. If you put Mount Everest into the Challenger Deep, there still would be 2 192 metres left before you broke the surface.

What's the Ocean Made of?

Most sea water (97.5%) is just that – water – but the rest is dissolved salts. While the most common salt in the ocean is "table salt", made of sodium and chloride, salts also include compounds formed from various other constituents, such as sulfate, magnesium, calcium and potassium. In fact, sea water is a sort of "Earth Tea", containing the dissolved atoms of probably every element on our planet. And while the most abundant elements in sea water are chloride and sodium, every cupful contains all the other elements, including such exotics as gold, silver and uranium.

So, why is the sea salty? First it's salty because rivers dissolve and bring down bits of the earth's crust and have been busily doing so for billions of years. Even thought rivers are "fresh", they contain minute amounts of dissolved elements. But if you take river water and concentrate its salts, they are not in the same proportion as the salts in the ocean. River water has too little chloride. In other words, there is too little table salt in river water to explain its concentration in the ocean.

Fortunately, scientists have recently discovered another major source of the elements for the ocean – the Earth's mantle.

The molten part of the Earth's mantle comes to the surface as lava and hot gas. Since the ocean covers 71% of the Earth's surface, most volcanoes and gas vents are under water, and the materials that escape into the ocean are similar to the chemical composition of the sea. In particular, hot-water vents are a source of mineral-rich water. Hot-water vents occur when ocean water seeps into volcanic fissures, encounter subterranean magma, and return to the ocean loaded with chloride (and hot!).

So, the best explanation for the large amounts of salt in the sea is that much of the sodium in the ocean comes from rivers dissolving away the Earth's crust, and much of the chloride comes form volcanic vents under the sea.

All of the salt we put on our food originates, one way of another, in the ocean. Worldwide, about one-third of our salt reserves are produced in huge evaporation ponds situated near salt water. The remainder comes from salt mines that recover salt laid down by the evaporation of ancient seas.⁴ Since salt originally came from the ocean, what is the difference between "table salt" and "sea salt"? Table salt is almost pure sodium chloride. When salt manufacturers evaporate sea water, the first salt that comes out is calcite (calcium chloride). When this occurs, the brine is shifted to another pond, more evaporation occurs and gypsum (calcium sulphate) precipitates out. What is left in the brine is primarily sodium chloride, or table salt. Sea salt retains all of the other salts.

Life in the Ocean

For all its size, most of the ocean's life is concentrated in a very small portion, near the surface and in the shallow waters near coastlines. First, remember that most life in the water ultimately depends on sunlight. This is because the bottom of the food web is made up of plants, and these need light in order to survive. Even in very clear water, sunlight only penetrates a short distance, maybe 30 metres or so.

The layer of ocean where light penetrates is called the photic zone; this is where most of the action takes place. Since plants require sunlight for survival, all plants live in the photic zone.

The other reason most life lives in shallow water is that it is there that most plant nutrients are concentrated. Many of these nutrients (such as nitrates) are carried from the land by water (in rivers, for instance) and tend to stay near the coast. However, in a few select locations, plant nutrients are extremely concentrated, and here is where life really gets going. These are called upwelling areas.

Upwelling

Upwelling is an extremely important process, one that has a profound effect on the productivity of the ocean. Upwelling is the process in which deep, cold, nutrient-rich water comes up to replace surface waters as they are moved offshore by winds. Most upwelling occurs along coastlines, and only a few coastlines at that. Major upwelling occurs along the coasts of California, Peru, Chile, West Africa and a few other scattered spots.

What effect does upwelling have? Well, first remember that microscopic plants (phytoplankton) absorb dissolved nutrients (such as nitrogen) from the water. Plants live near the ocean's surface, so surface waters tend to be low in nutrients. On the other hand, deeper water has little phytoplankton and, therefore, lots of nutrients. When this nutrient-rich water hits the surface, phytoplankton starts reproducing. Phytoplankton forms the basis for most ocean food webs, and the more phytoplankton there is, the more phytoplankton eater can live in the system. For this reason, upwelling areas usually contain more organisms (by numbers or weight) than any other open ocean habitat.

Activities

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Drop in the Bucket

Grades 5, 6 – Science, English Language Arts, Social Studies

Purpose

Students will investigate the source(s) of the water they use.

Water covers three-quarters of Earth's total surface, but less than half of one percent is available fresh water. An estimated 97.5% is seawater, another 2% is locked in polar icecaps and glaciers, and the rest of the unavailable water is trapped deep below the Earth's surface. Available fresh water comes from many sources: surface rivers, streams, lakes; underground reservoirs or water tables; collected rainwater; and purified seawater.

Materials

• information and material about your students' water supply or supplies. See resource section of this document for some suggestions of where to find this information.
• local travel map showing bodies of water

Procedure

Have students work in groups to read and review the materials you have collected. Can they determine the water supply of their own or a local town? How many litres of water per day does the population of that town need?

The students may also determine the source of their own drinking water if they live in a rural area that is not served by a municipal water authority. How many litres of water does their water source supply (over a specified time period)? How many litres of water does their family extract from the source?

Have the students choose a local industry for examination. How does the industry use water?

Is there an emergency water supply to which the students' town or families may turn in case of drought? How would the town or their family cope with a drought of several days' duration?

Extensions

To help explore some of the issues concerning water and water rights, have students discuss facts as a panel. Designate two groups as municipal government or water officials. Designate others to act as representatives of water users: residential, commercial, agricultural, and industrial.

Discuss certain issues (for example: drought, new business coming in, a new dam to be located upstream, local habitat loss) that require reallocation of water from existing supplies.

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Simulate the Hydrologic Cycle

Grades 4, 5, 6 – Multi-disciplinary

Lead your class through a hydrologic cycle. Help your students visualize the movement of water by having each student draw and label his/her own hydrologic cycle on a piece of paper. Have your students think of experiments they could set up to show how water moves through the hydrologic cycle. Here are some suggested experiments:

1. Place a pan or pans of water in a sunny area of the classroom. The water will evaporate. The larger the surface area of water exposed to the air and sunlight, the greater the rate of evaporation.
   
   
2. Leave a humidifier running in the room and watch the condensation form on the windows.
   
   
3. Fill a tray with soil (sand will allow faster response). At one end of the tray, drill an outlet hole. Place a container below the outlet. Elevate one end of the tray slightly. Now, sprinkle water on the elevated end, allowing the water to soak into the soil. Some of the water will run off, forming a channel; the rest will move throughout the soil the length of the tray and eventually flow out of the opening into the container. This demonstration will show runoff, groundwater recharge, groundwater movement and storage, and discharge to a surface water body.

Tell your students that there is a great deal of water moving around the earth in the air, through the ground, in the rivers, etc.; however, the percentage of water stored in major sources (for example, oceans, seas, etc.) Remains relatively constant.

You can also tell your students that the Earth has the same amount of water today as it did a million years ago. People merely use it and pass it on. This should not be interpreted to mean that people haven't changed the quality of some of the Earth's water. Over many years of using water, some of the water has been contaminated. It can be concluded that the earth has the same amount of water, but some of the water is not suitable for use any longer. This reduces the amount of water available for human and animal water use.

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Nature's Waterwheel

Grades 4, 5, 6 – Science

Purpose

Students will identify and describe what groundwater is, and will be able to identify and describe how the hydrologic cycle operates.

Hydrology is the study of the movement and distribution of the waters of the Earth. In nature, water circulates through a system called the water cycle or hydrologic cycle. This cycle begins when heat from the sun causes ocean water to evaporate and become water vapour. The atmosphere holds this water vapour while it gradually cools and condenses to form clouds. The water eventually falls as precipitation in the form of rain or snow. Most rain and snow falls back into the oceans, but some falls on the land and eventually either flows back to the seas or soaks into the land (percolation). The water which percolates into the ground is known as groundwater, and it is eventually used by nature and either transpired or evaporated into the atmosphere, completing the cycle.

There are two main sources of fresh water on Earth: groundwater and surface water. Surface water flows over the land in the form of lakes, rivers, and streams. Groundwater seeps through the soil or through cracks and cavities in rock. Groundwater is the source of water for wells and springs, and provides approximately 50% of the drinking water to Nova Scotian homes. Most rural areas depend heavily upon groundwater for their needs. Groundwater may be formed when precipitation percolates through the soil or when water from lakes and ponds seeps into the ground.

A layer or bed of porous earth materials which yields useful amounts of groundwater is called an aquifer. Wells are drilled down to an aquifer to draw groundwater to the surface. The surface of the aquifer is referred to as the water table.

If we draw more water from the aquifer than can be naturally recharged, then the water table is said to "drop". Many regions of the world are using up their groundwater supplies quicker than they can be recharged. This process is called water mining. Lowering the water table causes special problems in coastal areas, because salt water from the ocean can enter reservoirs of groundwater if the buffer zone is diminished.

Pollution of groundwater is a serious problem, particularly near cities and industrial sites. Pollutants that seep into the ground can come from contaminated surface water, leaks from sewage pipes and septic tanks, and from gasoline and chemical spills, among other things. Groundwater may also be polluted by chemical fertilizers and buried radioactive wastes.

Materials

• water
• hot plate
• tin or aluminum pie pan (the smaller, the better!)
• ice cubes
• Worksheets #1 and #2
• glass jar (such as a large mayonnaise jar) or glass pot (Visions pots work well)

Procedure

1. Place ice cubes in the pie pan to begin cooling the pan.
2. Place the jar or pot of water on the hot plate and wait for it to boil.
3. While waiting for the water to boil, pass out Worksheet #1. Read together and discuss.
4. Hold the pan of ice cubes over the steam from the boiling water. Steam from the boiling water condenses when it hits the cold ice cube pan. The condensed water then falls back to be changed to steam again, creating a water or hydrologic cycle.
5. Discuss the demonstration relating to Worksheet #1. Discuss how water seeps or infiltrates into the soil creating (and adding to, or recharging) groundwater.
6. Pass out Worksheet #2. Ask the students to complete Worksheet #2 from memory.

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The Water Cycle

Grades 4, 5, 6 – Science

Purpose

To create a student-sized example of the water cycle in action. This activity may be performed in sections, but requires a significant time commitment (seed germination). It is best performed when worked into a curriculum plan.

All of the water on Earth goes through a cycle in which the water changes its location or physical state through different processes. In accordance with the law of conservation of matter, water is not created or destroyed by this cycle: it just changes its form. Water can be found in all three states of matter during the cycle: solid (ice caps), liquid (lakes), and gaseous (water vapour). There are five processes by which water moves through the cycle:

1. Water in oceans and lakes evaporates into the air.
   
   
2. Cool air in the atmosphere causes the water vapour in the air to condense into a cloud.
   
   
3. Precipitation from the cloud falls to the ground as rain, sleet or snow, depending on the air temperature and atmospheric conditions.
   
   
4. The water on the ground percolates throughout the soil and some of it is absorbed by plants.
   
   
5. As plants go through photosynthesis (converting water, sunlight and carbon dioxide to form their own food), they absorb water from the soil and release some of it back into the air through transpiration.

These patterns of change can vary, but the cycle occurs continuously. Water has been cycling by means of these processes since the beginning of time.

Materials

• Three 2  litre pop bottles (with caps)
• Crayon or marker to mark plastic bottles
• Scissors
• String
• Empty film canister

Procedure

1. Remove the labels from the bottles.
2. Draw a line with marker or crayon just below the "shoulder" of bottle A, as indicated in the diagram (right), keeping the line at the same height on the bottle all the way around.
3. Using the same method outlined in (2.), cut bottles B and C just above the "hips", as indicated in the diagram (right).
4. Poke a hole in one bottle cap using an awl or a pin. The hole should be just large enough to thread your string through it. Place this cap on bottle B.
5. Cut a 40 cm length of string. Fold the string in half and insert the folded end through the cap hole to make a loop inside. Leave at least 5 cm of each end of the string hanging down from the cap.
6. Place a cap with no hole on bottle C. Tie 20 cm of string around the bottle neck, so that one end hangs down about 7 cm.
7. Assemble the bottle column: B inserts into A; C inserts into B. These three parts of your model will be referred to as "chambers" for the rest of the activity.

Create a Bottle Environment

1. Wet both strings thoroughly. Add 150 ml of water to Chamber A. This will be the water source for the cycle.
2. Fill Chamber B with enough moist soil to cover the loop of string (about 200 ml will do). The string should run up into the soil, and not be pressed against the side of the column (the students will not be able to see the string running through the soil).
3. Plant several fast-growing, hardy plant seeds in the soil around the sides of Chamber B. While the seeds are germinating, leave Chamber C off – this will help with air circulation and help the seeds grow.
4. Place the film canister (or another bottle cap if you don't have a film canister) on top of the soil at the centre of Chamber B so that the wick tied to Chamber C hangs into it. If the film can will not fit between Chamber C and the soil, trim it with scissors. This is your rain collector.
5. Once your plants have germinated, place Chamber C back on Chamber B and fill C with ice water.
6. The students are ready to draw the water cycle column and to begin filling in their observation sheets (Observation sheet #1 and Observation sheet #2). Your finished water cycle column should look like this diagram:

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Diary of a Water Molecule

Grades 4, 5, 6 – English Language Arts, Science, Social Studies, Art

Purpose

Students will trace a water molecule's journey through the hydrologic cycle by writing a story about one molecule.

Water is the most abundant liquid in the world. It is also constant – we have the same amount of water on this planet today as we had millions of years ago! Water is continually being cycled through the hydrologic cycle – via evaporation, transpiration, condensation, percolation, precipitation. The water we drink today could have been part of the ocean when Port Royal was established, or it could have been part of a dinosaur's bath!

Materials

• looseleaf paper
• pencils / pens

Procedure

It might be mood-enhancing to play some water-related symphonic or instrumental music (softly) in the background as the students write.

Ask the students to image that they are a drop of water. They are to write a story about their life as a water molecule. The composition could take the form of a diary of where they have been in the past; a science-fiction, futuristic story about this molecule's experiences in the 24^th Century; a description of how it feels to be part of the Atlantic Ocean, or a thunderstorm or a snowflake... whatever their imagination decides.

Set aside a period of at least 15 minutes for them to write their stories, and another period of time if you wish to have them illustrate their compositions. You may want to set aside a couple of time periods during the week so that they may successfully complete their story (they may take as long as the first period simply to decide which aspect of water they wish to portray and jot down some relevant/salient points to include in their compositions).

Extension

Use the stories and drawing created in a bulletin board about the water cycle.

Creative students may wish to write and perform a play about a water molecule for younger students in the school.

Some of the bolder students may read their works to the class or to other classes and/or other grades.

Include the compositions in a Water Book.

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How Wet is Our Planet?

Grade 6 – Mathematics, Science

Purpose

Students will be able to describe the amount and distribution of water on the earth in oceans, rivers, lakes, groundwater, ice caps, and the atmosphere; students will make inferences about the importance of responsible water use.

The Earth has been called the water planet. Between two-thirds and three-fourths of its surface is water. The Earth's water can be seen in flowing rivers, ponds, lakes, oceans, locked it he northern and southern ice caps, and drifting through the air as clouds. Water that has seeped into the earth's crust (groundwater) is more difficult to see, yet all these forms of water are part of a dynamic, interrelated flow that we call the water cycle.

Each of the segments of the water cycle share a portion of the total amount of water on the planet. Students tend to think of water as being limitless, and yet simple calculations will demonstrate the fact that the amount of water on Earth is limited. Scientists believe that all the water we will ever have is on the Earth right now, and has been since the time of the dinosaurs. Whatever amount of water is available to humans and wildlife depends largely on how its quality is maintained. Human beings must act, individually and collectively, as stewards of this vital resource, conserving water, using it wisely, and protecting its quality.

The purpose of this activity is for students to acquire an understanding of how fragile a resource water is.

Materials:

• large display map of the world
• globe (one showing the ocean bottom is best)
• aquarium
• pens/pencils
• calculators
• measuring cup
• 2-litre container for every three students
• measuring tablespoon (market in ml) for every three students

Procedure

1. Using a map of the Earth, begin a discussion of how much water is present on the planet. Ask students to comment on why the earth is called "the water planet". Call the students' attention to the statistic that between two-thirds and three-fourths of the surface of the Earth is covered with water. After general discussion, provide the students with the following percentages:
   
   Water on Earth:
   Oceans – 96.5%
   All ice caps/glaciers – 1.7%
   Groundwater – 1.6%
   Freshwater lakes – 0.007%
   Inland seas/salt lakes – 0.006%
   Atmosphere – 0.001%
   Rivers – 0.0002%
   Total – 99.8132%
   
   
2. Discuss the relative percentages. Do the calculations for them, or ask the students to calculate the estimated amount of fresh water potentially available for human use:
   
   Water Potentially Available for Human Use:
   Groundwater – 1.6%
   Freshwater lakes – 0.007%
   Rivers – 0.0002%
   Total – 1.6072%
   Adding ice caps/glaciers – 1.7%
   Total – 3.3072%
   
   
3. Discuss these figures, emphasizing that the usable percentage of existing fresh water can be reduced by pollution and contamination. Also, all groundwater is not available and ice caps certainly are not readily available. Discuss the need of humans for usable fresh water. Ask the students to consider what other life forms need both fresh and salt water.
   
   
4. Show the students 5 gallons (23 litres) of water in an aquarium. Tell them how much is in the aquarium. Provide the student with the following quantity: 5 gallons = 1280 tablespoons.
   
   
5. Have the students assume that the five gallons represent all the water on earth. Do the calculations for them or ask the students to calculate the volume of all the other quantities on the water percentage list. This will require the use of decimals. Remind the students that for multiplication all the decimal places must be shifted two places to the left so that the 97.2% becomes 0.972 before they multiply. For example: 0.972 x 1290 tablespoons = 1244.16 tablespoons.
   
   
6. Once the values are obtained, ask the students to calculate the volume of the water other than ocean water (it is approximately 34 tablespoons). Ask them to divide up in teams of three and put 34 tablespoons of water in a container and take it to their workplaces.
   
   
7. At their workstations, ask the students to remove the amount of water represented by all freshwater lakes and rivers (it is 0.11 tablespoons, approximately on-tenth of a tablespoon). This is less than a drop. Discuss the relative proportions with the students.
   
   
8. Consider the fragile nature of the freshwater, wetlands and oceans of our planet. Discuss how all species depend upon this minute percentage of water for their survival. Summarize the activity by using an Earth globe to illustrate that if the Earth were "this size" – the size of the glove – less than on-half cup (eight tablespoons) of water would fill all the oceans, rivers, lakes and ice caps. Also, emphasizing the importance of keeping the Earth's waters clean and healthy and when we do use water, using it wisely and responsibly.

Extensions

Ask the students to estimate the percentage of water that is distributed in each of the following areas of our planet: oceans, rivers, freshwater lakes, inland seas and saltwater lakes, groundwater, ice caps and glaciers and the atmosphere. Why is it important that humans use water responsibly?

Create a mural of the water cycle that graphically includes statistics which represent the relative amount of water in each component of the cycle. Calculate how much pollution is entering our waterways each year. The Information Please Almanac and The Cousteau Almanac are excellent resources for such information.

Calculate the size of a model of the earth that would accommodate all the water in the aquarium used in the demonstration.

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Notes:

1. 1982 statistic.
2. 1992 statistic.
3. Excerpted from the Teacher's Guide to the IMAX film, "The Living Sea".
4. One such mine exists at Pugwash, Nova Scotia.

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