For Students
Engineering Design in Oregon Science Classrooms
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Filled Data Table Handout for Bioswales
Introduction: In the next part of this lesson, you will be designing water filters. For your filter you will need
to decide on the amount, combination, and sequence of materials that will best clean polluted water. Knowing
the filtration abilities of cheesecloth, sand, gravel, rock, and limestone will help you determine these values.
(Note: In this water filter model the cheesecloth represents plant roots.)
Turbidity is a measure of the cloudiness of a liquid caused by solid particles. If these particles are
large, they generally settle to the bottom of the liquid. However, smaller particles too tiny to see with the naked
eye stay suspended, discoloring the liquid, just like smoke particles float in the air and make it hazy. Since high
turbidity in water is a sign there are many foreign substances mixed in, it is a key test of water quality.
Pure water has a pH close to 7 at room temperature. Deviations from this neutral pH indicate the
presence of chemicals in the water. Acidic substances like sulfuric acid and many types of fertilizers will
decrease the pH value, while alkaline substances — soaps, bleach, and calcium carbonate (limestone and Tums)
— increase water’s pH value. Although natural water systems are usually slightly acidic or slightly basic, they
are safe. But pollution may cause too much deviation from neutral, and the environment suffers because most
aquatic animals and plants have adapted to life in water with a specific, narrow pH range. That is why pH is
another good test of water quality.
Filter Material
2.5cm x2.5cm
Cheesecloth
Square
(4 ply)
1/3 Cup Sand &
Cheesecloth
Square
Infiltration
Time
Change in
Turbidity
Change in pH
Observations
Tea particles caught in cheesecloth.
10.24 sec
0
0
Cheesecloth stained green.
Takes a moment for solution to
begin dripping
5.82 min
+7
0
Tea particles caught in sand.
Sand has green tint after filtration
1/3 Cup Gravel
& Cheesecloth
Square
23.83 sec
0
0
Tea particles caught in gravel.
1/3 Cup Rocks
& Cheesecloth
Square
17.82 sec
0
0
Tea particles caught in rocks.
1/3 Cup
Limestone &
Cheesecloth
Square
Did not filter enough to measure
turbidity.
-
-
+1
Tea particles caught in limestone.
Becomes more grey and somewhat
turbid.