Water: Is it Safe to Drink?
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

National Academy of Sciences
Standards Addressed:
As a result of activities in grades 9-12,
all students should develop
understandings of the following
    •   personal and community health;
    •   environmental quality;
    •   scientific inquiry;
    •   natural resources;
    •   natural and human-induced

Desired Outcomes:
After completing the lesson, students
    »   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

Class Time:
45 - 90 minutes

Materials Needed:
    •   5-gallon aquarium or large, clear
       container filled with clear tap
    •   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
   •   appropriate lab safety equipment;
   •   Safe Drinking Water Act poster;
   »   observation sheet (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
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

    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

       Table 1: Filter Construction
Figure 1: Filter Construction
   Filter Materials
   Filter 1. funnel lined or covered with pantyhose
  Filter 2. funnel, pantyhose, cotton balls
  Filter 3. funnel, pantyhose, cotton balls, coffee
  Filter 4. funnel, pantyhose, cotton balls, coffee
         filter, activated charcoal   	
  Filter 5. runnel, pantyhose, cotton balls, coffee
         filter, activated charcoal, sand	

cotton balls

coffee filter

activated charcoal
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
    •   Why is it good to have materials
       of different sizes or textures in a
       filter? [The advantage of having
       materials with different size

       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
   •   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
                           >  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

                       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

Lab Activity: Filtering a Water Supply

Name:     	_j»	
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

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
Filter Materials
pantyhose, cotton
pantyhose, cotton
balls, coffee filter
pantyhose, cotton
balls, coffee filter,
activated charcoal
pantyhose, cotton
balls, coffee filter,
activated charcoal,
Observations: How effective was each filter?