Water: Is it Safe to Drink?
Objectives:
Students will construct, use, and
compare simple filters to attempt to
purify polluted water. Students also will
use the Safe Drinking Water Act poster
to predict and prevent the effect of water
pollution on their community's drinking
water.
National Academy of Sciences
Standards Addressed:
As a result of activities in grades 9-12,
all students should develop
understandings of the following
concepts:
• personal and community health;
• environmental quality;
• scientific inquiry;
• natural resources;
• natural and human-induced
hazards.
Desired Outcomes:
After completing the lesson, students
will:
» recognize the source(s) of their
community's drinking water;
» understand the potential threats
to their drinking water;
• recognize their role in protecting
their drinking water at its
source(s).
Class Time:
45 - 90 minutes
Materials Needed:
• 5-gallon aquarium or large, clear
container filled with clear tap
water;
• 1 Ib. dirt or sand;
• 1 Ib. leaf litter or grass clippings;
» 1 cup gasoline;
• 1 drop or cup motor oil;
• 1 cup dissolved fertilizer;
• 1 cup pesticide;
• small trash items;
• for every 2-3 students: clear
plastic 2-liter bottle, plastic
funnel (each of which can be cut
from other 2-liter bottles),
pantyhose, cotton balls, coffee
filter paper, activated charcoal,
and clean sand (see Figure 1
below);
• appropriate lab safety equipment;
• Safe Drinking Water Act poster;
» observation sheet (reproducible).
Reproducible:
• Filtering a Water Supply: This
handout contains a table on
which students should record lab
observations and results.
Lesson Steps:
1. Describe a sunny day at the local
river, lake, or other source from
which your community draws its
drinking water. Then ask students
whether activities they enjoy in or
around that source could potentially
threaten their drinking water. You
could ask students "Has anyone
taken a car ride on a road beside a
lake?"
2. Add a small drop or cup of motor oil
to the demonstration water supply,
and ask students to infer why you did
this after having asked your question.
3. Ask students for other possible
pollutants and continue to add
pollutants you have prepared. By the
. end of the demonstration you should
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be able to point out several things:
The water looks different (physical
pollution should be visible); not all
sources of chemical pollution
(gasoline, fertilizer runoff) may be
visible; and the water no longer is
safe to drink.
4. For dramatic effect, pour some of
this polluted water into a drinking
glass and ask students whether they
would drink the water. After they say
"no," tell students that all these
pollutants potentially threaten their
drinking water (although not
necessarily in the same quantities as
used during the demonstration.)
5. Divide the class into pairs or trios.
Give each group one clear plastic 2-
liter bottle and a funnel, or have
them make a funnel from another 2-
liter bottle by simply cutting a 2-liter
bottle in half and discarding the
bottom half. Label each bottle with
the group number.
6. Explain to the class that each group
will build one of five slightly
different filters. Each filter will be
used in an attempt to decontaminate
the same polluted water supply. Use
Table 1 to assign the different filters
to each group. Use Figure 1 to see
how the most complex filter might
look.
Table 1: Filter Construction
Figure 1: Filter Construction
Filter Materials
Filter 1. funnel lined or covered with pantyhose
only
Filter 2. funnel, pantyhose, cotton balls
Filter 3. funnel, pantyhose, cotton balls, coffee
filter
Filter 4. funnel, pantyhose, cotton balls, coffee
filter, activated charcoal
Filter 5. runnel, pantyhose, cotton balls, coffee
filter, activated charcoal, sand
pantyhose
cotton balls
coffee filter
activated charcoal
sand
—Ws&B&Y
7. Make sure each group covers the top
or bottom of the funnel so large
particles will be-caught. For
example, the pantyhose should be
stretched across the top of the filter
and the coffee filter should be
opened up to line the bottom of the
filter (see Figure 1).
8. Once all filters have been
constructed and each has been placed
on top of a bottle, stir the polluted
water supply and pour the same
amount of polluted water through
each filter.
9. Have students observe the results
and record, their observations on the
reproducible. Students should
compare the original polluted water
to each filtered bottle.
Note: Please do not pour any pollutants
down the drain!
10. Discussion Questions:
• Which type of filter appeared to
work best and why? [The most
complex filter worked the best
because it contained materials
of many different sizes to catch
or remove different-sized
particles from the polluted
water.]
• Why is it good to have materials
of different sizes or textures in a
filter? [The advantage of having
materials with different size
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pores in a filter is so all the
various-sized particles
suspended in the water supply
can be removed. If a filter just
used the smallest-sized pores
(like the coffee filter's), then it
might become clogged with
larger particles and not work
as effectively.]
• What pollutants did the filter
materials obviously capture? [It
captured objects suspended in
the water like trash, grass, leaf
litter, sand, and oil.]
• What pollutants got through the
filter materials? [Objects that
dissolve in the water or that are
small enough to pass through
the filter pores like dissolved
fertilizer or gasoline. Students
may need to smell the filtered
water to detect these
substances.]
• What else might you need to do
to the water used in this
experiment before it is potable
(drinkable)? [Before drinking
this water you still would want
to try to remove any gasoline
or high levels of chemicals
dissolved in the water. The
water also may need to be
chemically treated to kill any
harmful microorganisms.]
11. Using the poster as a
springboard, students first should
identify and describe potential
drinking water threats on the poster
(in red), and then do the same in
their community.
12. Helopstudents recognize their
roles in protecting drinking water at
its source. Assign students any of the
Academic Extensions below:
> Stage a mock town meeting.
Invite a water treatment facility
manager to discuss how
pollutants such as those used
during the lab are removed from
drinking water.
> Research how polluted water
affects people's health, and
discuss these issues with local
leaders.
> Create a pamphlet to teach
community members how to
prevent potential threats to
drinking water.
> Tour a local water treatment
facility. Compare your lab filters
to the plant's filtration system.
> Research the most deadly
pollutants that can be found in a
drinking water source. Are there
any lakes or rivers in your state
that have warnings for high
amounts of these materials?
> Create a poster, similar to the one
used in class, that represents your
community.
Additional Resources On:
Safe Drinking Water
http://www.epa. gov/safewater/
This EPA Web site provides information
about local drinking water quality and
source water protection.
Office of Water
EPA 816-F-02-015 www.epa.gov/safewater August 2002
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Lab Activity: Filtering a Water Supply
Name: _j»
Date:
Background: Filtering is the process of removing solids from water. People must filter
water sources for many reasons. Some chemicals found in water supplies can make
humans or pets sick. Many of the organic materials found suspended in water supplies
provide surfaces or nourishment for harmful bacteria or other microorganisms. After
water is filtered, it usually is treated with chemicals such as chlorine to kill potentially
harmful microorganisms. Filters can be constructed with simple materials to
demonstrate the effectiveness of filtering systems in removing pollutants from water
supplies.
Purpose: to construct, use, and compare filtering systems to observe how water is
filtered of pollutants. Each group will construct a slightly more complex filter. Students
then will record observations and compare results.
Observations and Results: Effectiveness of Various Types of Filters
Group
1
2
3
4
5
Filter Materials
pantyhose
pantyhose, cotton
balls
pantyhose, cotton
balls, coffee filter
pantyhose, cotton
balls, coffee filter,
activated charcoal
pantyhose, cotton
balls, coffee filter,
activated charcoal,
sand
Observations: How effective was each filter?
.
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