Engineering grand
challenge:
Providing clean
water!
Name:
Date:
Background Information:
When Samuel Taylor Coleridge wrote “water, water,
everywhere, nor any drop to drink,” he did not have the 21st
century’s global water situation in mind. But allowing for
poetic license, he wasn’t far from correct. Today, the
availability of water for drinking and other uses is a critical
problem in many areas of the world.
Lack of clean water is responsible for more deaths in the world
than war. About 1 out of every 6 people living today do not
have adequate access to water, and more than double that
number lack basic sanitation, for which water is needed. In
some countries, half the population does not have access to
safe drinking water, and hence is afflicted with poor health. By
some estimates, each day nearly 5,000 children worldwide die
from diarrhea-related diseases, a toll that would drop
dramatically if sufficient water for sanitation was available. In
some developing countries, water supplies are contaminated
not only by the people discharging toxic contaminants, but
also by arsenic and other naturally occurring poisonous
pollutants found in groundwater aquifers.
Household-scale filters are considered to be one of the most
promising options for providing clean water to communities
across the globe. Today, you will design and build your own
water filter.
Purpose: Millions of people rely solely on groundwater for their drinking
water, and nearly everyone relies on groundwater to irrigate
farmland. Water is filtered as it flows through the ground, but the type of
material through which it flows and the length of flow vary considerably.
Even municipal water systems have limited ability to filter water, particularly
when the type of contaminant is unknown.
Design phase: You will have the following materials available for your
filtration system:
Materials:
• 2-liter plastic bottle
• scissors
• coffee filters
• rubber bands
• filtration materials – soil, sand, gravel, marbles, cotton balls, vegetation
(shredded lettuce)
You may choose up to 3 filtration materials, and you may use them in any
order.
Things to remember:
 These systems will be built within plastic bottles like the one
your teacher has as a sample. The bottom will be cut off, and a
screen will prevent the small opening from spilling filtration
materials. Your system will include 3 of the filtration materials
provided to you.
 You will not know what is in the polluted water until after your
system is constructed.
 Review the competition/grading rubric as you design. Note that
you will receive points based both on the purity of the water
that passes through your filter, as well as how fast your will
pass through your filter. Water purity is weighted more, and
should therefore be the focus of your thoughts. However, if your sample
does not pass through your filter system in 15 minutes, your
team is disqualified and will not earn points for water purity.
 You will also be evaluated on your attitude, team cooperation, timemanagement and overall contribution to your group.
 Your design should consist of a simple sketch and a short
paragraph describing why you used the materials you did, and
how the order was chosen on the paper provided. Hand in the design to
your teacher.
 Discuss the details of your design to your class. At this point
the teacher will be holding everyone’s designs, so there is no
worry of someone stealing your ideas.
Paragraph describing why you choose the materials you did, and how the
order was chosen:
Water Filtration Rubric:
CATEGORY
4
Water Quality Very clear, no
particles
Time
0-60 seconds
3
Clear, some
small particles
remaining
61-120 seconds
2
Murky, large
particles
remaining
121-180
seconds
1
No noticeable
change from
start
>181 seconds
Participation Rubric:
CATEGORY
Attitude
4
Never publicly
critical of the
project or the work
of others. Always
positive about the
task(s).
3
Rarely publicly
critical of the
project or the work
of others. Often
positive about the
task(s).
2
Occasionally
publicly critical of
the project or the
work of others.
Usually positive
about the task(s).
1
Often publicly
critical of the
project or the work
of others. Often
negative about the
task(s).
Team
Cooperation
Almost always
listens to, shares
with, and supports
the efforts of
others. Tries to
keep people
working well
together.
Usually listens to,
shares, with, and
supports the efforts
of others. Does not
cause "waves" in
the group.
Often listens to,
shares with, and
supports the efforts
of others, but
sometimes is not a
good team
member.
Rarely listens to,
shares with, and
supports the efforts
of others. Often is
not a good team
player.
Timemanagement
Routinely uses
time well
throughout the
lesson to ensure
things get done on
time. Group does
not have to adjust
deadlines or work
responsibilities
because of this
person's
procrastination.
Usually uses time
well throughout
the lessons, but
may have
procrastinated on
one thing. Group
does not have to
adjust deadlines or
work
responsibilities
because of this
person's
procrastination.
Tends to
procrastinate, but
always gets tasks
done by the
deadlines. Group
does not have to
adjust deadlines or
work
responsibilities
because of this
person's
procrastination.
Rarely gets tasks
done by the
deadlines AND
group has to adjust
deadlines or work
responsibilities
because of this
person's
inadequate time
management.
Contributions
Routinely provides
useful ideas to the
team. A definite
leader who
contributes a lot of
effort.
Usually provides
useful ideas to the
team. A strong
group member
who tries hard!
Sometimes
provides useful
ideas to the team.
A satisfactory
group member
who does what is
required.
Rarely provides
useful ideas to the
team. May refuse
to participate or
give up at times.
Build phase:
o Cut the top off of your plastic bottle.
o Remove the cap, and rubber band the coffee filter around the neck of the
bottle. Turn the top upside down and place in the plastic bottle.
o Create your filtration system just as you designed. Each layer
should be about 2 inches thick.
Testing phase:
o Get a sample of water from your teacher. Describe the water (how does
it look, smell, what color is it, etc):
o Before pouring the polluted sample through your filter, be
prepared to
1) start timing to see how long it takes to move through your filter.
2) collect the water flowing through your system.
o You may only filter your water once.
o Raise your hand and the teacher will come score your finished water
based on the rubric.
5. Follow-up.
o Complete the follow-up sheet.
Name: ________________________Date: ____________________
Water Filtration
Follow-up Questions
1. Which of the filtration materials was most effective at filtering your
polluted water? Explain why you think this material was the best.
2. If you were to retest with the same polluted water, what changes would
you make to your filtration system? (Nothing is not an acceptable answeryou can always improve!)
3. Do you think the order in which you placed your filtering materials made
any difference?
Explain why or why not.
4. What other objects do you think would improve the physical filtration of
the systems built in class?
5. Engineers are constantly working to improve water filtration systems. Why
is it important to have clean water?
6. Brainstorm: List two other ways we can provide clean water to place
where there isn’t any:
7. Evaluate your contribution to the group:
Analytical Instruments:

Spectrophotometer—we will use this to measure the amount of particles in
suspension. The spectrophotometer can measure the attenuation of a light
beam due to scattering (deflection of light from a straight path) or absorption
(uptake of light by medium)—here we will assume that light attenuation is due
to scattering off particles and that the amount of light lost from the beam is
proportional to the amount of solid material in suspension. It will be necessary
to teach the students how to use the spectrophotometer. Light scattering is
usually measured at relatively long wavelengths, where there is little loss of light
due to absorption by dissolved material in water. Here, I recommend a
wavelength of λ = 640 nm (nanometers). The spectrophotometer will give you a
measurement called absorbance or optical density. At relatively low particle
densities, absorbance is related to particle concentration by
A=εlc
where
A is the absorbance reading (here @ 640 nm)
l is the light pathlength across a cuvette that fits the instrument
(here 1 cm)
ε is a constant of proportionality
c is the particle concentration in the suspension
Figure 1. Schematic diagram of a single-beam spectrophotometer.

Spectrophotometer—Can also be used to measure light absorbance in the visible
range. Selective absorbance of light energy at specific wavelengths is what

produces color. Each color of food dye absorbs a different pattern of light
wavelengths in the visible light range. You might check this out in class.
Conductivity meter— A conductivity meter works by establishing a known
difference in electrical potential across a fixed distance. The fluid in the middle
can then conduct charge across that gap. Electrical conductivity (proportional to
the current between the electrodes) will be relatively high if there are lots of
ions in the fluid to conduct charge or if the fluid is itself polar—like water. Water
becomes more conductive as its salt content increases. Again, you might conduct
a little experiment measuring the conductivity of water as a function of total salt
that is dissolved in it.
Instructor Notes:
You can prepare your wastewater any way you like- feel free to be creative and add
additional elements! Our standard preparation includes cornstarch, food coloring and
salt. There is lots of background material that you could prepare and present regarding
the sustainability of water supply in the Southwest—who is using our water and where
does it come from? There are some scientific issues to expose as well—for example, the
mechanisms of particle removal during filtration, how to improve filter performance,
Beer’s law for measurement of dissolved organics, how to make a standard curve, etc.
All classes are encouraged to modify the experimental procedure as dictated by the
capabilities of the class, time restrictions and so forth.
Students should be asked to write up the results of their exercises using a standard
format—background and objectives (including the hypotheses to be tested, materials
and methods, results, and discussion of results. Perhaps the very best of the write ups
can then be used as models to show students what works and talk about how to
improve their own scientific writing.