Activity 2.1.1 Global Water Distribution
Introduction
Earth might be best called the water planet, as water covers roughly seven-tenths of
the Earth’s surface. Given there is so much available water, how much of this do you
think is readily accessible and suitable for human consumption? Surprisingly, the
answer is very little. In fact, not having sufficient clean drinking water is a major
issue in many parts of the world, including both the developing and industrialized
nations.
Many humans value Earth’s rivers and lakes as recreational opportunities; however,
nearly every living thing relies on them for survival. Free-flowing rivers provide
several necessities. They're an important source of drinking water and irrigation for
crops. They carry sediments that help create coastal wetland features such as
marshes that provide habitats for many animals and plants. Clean, flowing rivers
provide dissolved oxygen in the water that aquatic life and fish need to breath.
Pollution poses the largest threat to fresh water systems. Pesticides in agricultural
runoff unintentionally kill fresh water organisms, and raw sewage from municipal
sources spreads disease to people and animals that rely on the water. Protecting
rivers from pollution, however, isn't the only challenge to be met. Even though the
Earth's supply of fresh water is continually being renewed through the water cycle, it
is still in short supply in many places. Finding ways to conserve this precious
resource is of utmost importance.
In this activity you will use scientific estimates of the different types of water on Earth
to first calculate the relative amounts of each type of water as a percentage of all
water. You will represent the relative amounts of all of Earth’s water using an 18 liter
model. You will use a variety of laboratory measuring equipment to precisely
measure each type of water for this scaled down model in order to physically
determine the amount of freshwater that is available for human use compared to
total water sources.
Through this activity you will also learn to select appropriate volumetric measuring
equipment and develop skills for accurately and precisely measuring volume with
each type of measuring device.
Equipment
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2 - 5 gallon buckets
18 liters of water
1 - 1 L beaker
Graduated cylinders of various sizes (10 mL, 50 mL, 100 mL, 250 mL, 500
mL, 1000 mL)
1 - Transfer pipette (1.0 mL with 0.1 mL graduations)
(Optional) Pipette bulb or roller
(Optional) Serological pipette
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Environmental Sustainability Activity 2.1.1 Global Water Distribution – Page 1
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1 - Micropipette (0.5 L –10 L)
1 - Micropipette (20 L – 200 L)
Micropipette tips to fit micropipettes
Calculators or computer with Excel® or other spreadsheet software
Procedure
In your engineering notebook, write down your best estimate without
conducting any research of the percentage of all water on Earth that is suitable
and available for human consumption.
Look at all of the different sources of water shown on Table 1 below. Place a
checkmark in the last column next to what you think are the three most
common sources of human drinking water.
Calculate Percentages and Proportions - These calculations can be done
using a calculator and the chart on the next page or using the Excel
spreadsheet 2.2.1.A Global Water Distribution Excel.xlsx.
A. Using the data for each type and amount of water on Earth,
calculate the total water percentage of each type of water source
and record your calculations in Table 1.
B. Calculate the percentage of each freshwater (non-saline) source
compared to the total fresh water and record your calculations.
C. For the scaled-down water model in which 18.00 liters (L) of water
represents all of Earth’s water, calculate the proportional volume in
milliliters (mL) for each type of water. Record these values in Table
1. Check to make sure that the sum of all these proportional
calculations equals 18.00 L.
D. Total the amount of water available for human consumption in the
18 L scale model and record this figure in your engineering
notebook.
Select Measuring Equipment
A. View and take notes in your engineering notebook on the Measuring
Volume presentation.
B. Look at the volumes of water to be measured in 18 L scale model
and determine which type of laboratory measuring tool, from the list
of equipment available, should be used to most accurately and
precisely measure that volume. Record your choice and reasoning
in Table 1.
Complete Activity 2.1.1 Using a Micropipette Student Resource
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Environmental Sustainability Activity 2.1.1 Global Water Distribution – Page 2
Table 1: Global Distribution of Water
Water Source
Water Volume (km3)
Total Water
(%)
Fresh Water
(%)
18 L Scale Model
Proportional Volume
(mL)
Best Instrument for
Measuring Volume
√ if Common
Source for Human
Consumption
Saline Water
Oceans, Seas, and Bays
Groundwater: Saline
Lakes: Saline
Total Saline Water
1,338,000,000
12,870,000
85,400
1,350,955,400
Freshwater
Ice caps, Glaciers, and Permanent Snow
Soil Moisture
Ground Ice and Permafrost
24,064,000
16,500
300,000
Atmosphere
12,900
Swamp Water
11,470
Biological Water
Groundwater: Fresh
Rivers
Lakes: Fresh
Total Fresh Water
Total Global Water
1,120
10,530,000
2,120
91,000
35,029,110
1,385,984,510
Data Source: Igor Shiklomanov's chapter "World fresh water resources" in Peter H. Gleick (editor), 1993, Water in Crisis: A Guide to the World's Fresh
Water Resources (Oxford University Press, New York). http://ga.water.usgs.gov/edu/earthhowmuch.html
© 2015 Project Lead The Way, Inc.
Environmental Sustainability Activity 2.1.1 Global Water Distribution – Page 3
Measure Water Volumes for the 18 L Scale Model
A. Measure 18.00 liters of water into one of your 5 gallon buckets using
the measuring device that will provide the most accurate
measurement for this volume of water.
B. Using the proportional volume values that you calculated, use the
volumetric device you indicated as most suitable for each
measurement to accurately transfer that amount of water from the
full bucket to the empty bucket. Start with the saline water sources
and progressively move down through the freshwater sources. Stop
transferring the water after completing the “Biological Water”
measurement.
C. The amount of water remaining in the starting bucket represents the
percentage of all water out of all 18 L that is usable for human
consumption. Measure the volume of this consumable water and
record this measurement in your engineering notebook.
D. [Optional] If teacher demonstrates Steps 5 A and B, then each
student group will start with the same amount measured in step 5C
to measure the amount of freshwater.
[Optional] Use your Excel Spreadsheet data to create a chart to demonstrate
the distribution of the Earth’s water.
Conclusion
How did the amount of water you measured in the last step of the procedure
compare with the calculated sum of water available for human consumption
(fresh groundwater, fresh lakes, and rivers)? Explain why there might be
differences between the calculated volume and the actual measured volume.
What are the potential sources of error in this activity? What could be done to
minimize errors?
It was very similar in proportions, but massively smaller in actual size. There
might be differences in calculated volume and actual volume due to human
error and inaccuracies in filling the tank.
Explain how you chose the correct volumetric measuring instrument, such as a
beaker, a graduated cylinder, a pipette, or a micropipette.
I chose a graduated cylinder due to its superb capabilities of measuring liquids
accurately. I also chose the graduated cylinder due to it having a larger
capacity than the other available options.
How did your choice of different volumetric measuring instruments potentially
affect the accuracy and/or precision?
My choice of volumetric measuring instruments made my measurements more
accurate and reduced the chance of error.
Considering the percentage of usable fresh water, what should we be
concerned about when we use water?
We should be concerned about how we use water to preserve the amount of
drinkable water we have. This is because we have less than 2% of water on
earth available to drink. Only less than 1% is accessible.
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Environmental Sustainability Activity 2.1.1 Global Water Distribution – Page 4
Describe at least three other factors that might make availability of fresh water
for human consumption a challenge in different parts of the world.
Location of water- It can make it difficult to obtain said water.
Quality of water – Is it contaminated?
Amount of water – Is there enough for everyone to drink
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Environmental Sustainability Activity 2.1.1 Global Water Distribution – Page 5