REMOVING POLLUTION FROM WATER
PREWORK: Place each common item in a baggie or lidded cup. Label as the “pollutant” with 1
“pollutant” per child. Print datasheet. Make one filtering set-up for class demo at end.
crushed chalk – shellfish
wood shavings – trees
sand – land run-off
leaves
cake sprinkles – litter
food coloring – rain water mixed with car oil
corn starch – farmer’s fertilizer
vinegar – acid rain created from car exhaust
baking soda – household cleaning
soil – animal manure
molasses – human waste water
dirt – construction runoff
paper – litter
Styrofoam – litter
dish soap – laundry water
Kool-Aid – paint
corn syrup with food coloring – factory discharge
vegetable oil – motorboat fuel and oil
PURPOSE OF EXPERIMENT: Assess methods for removing pollution from water
INTRO: Ask students what they know about water. What water is clean? What water is dirty?
What makes water dirty? (Water Pollution) What is the Water Quality in the bodies of water near
where they live?
Where does our water come from? Where does the water in our local creeks, bayous, rivers,
ponds, and bay come from? (Watershed) Where does the water that comes through their pipes
come from? (Water supply; cleaning water for human consumption)
Where does water go? What happens to the water that goes in the drainage under the sidewalks?
What is the role of the settling ponds? What kinds of filters exist in nature? (Wetlands) What
happens when you flush the toilet? (Cleaning discharge from homes)
What is the first step of making clean water? (Filtration) Why would you need to filter water?
(Drinking or cleaning) What types of material can you use to filter the water?
PROCEDURE: Present clean water. Reserve some of the clean water to use as a standard and
pour the remainder into a pitcher. Display the filtering materials.
HYPOTHESIZE: Does the type of material used in a water filter affect how clean filtered water
becomes? How will the group determine if the water they make is clean? What debris will each
material filter out? Will one of the filtering materials work to remove all the debris?
Students fill in these two portions of the datasheet.
Distribute baggies/cups of “pollutants.” Have each student add the “pollutant” to the water. Start
with the more natural ones, like the wood chips, chalk, sands, and leaves. Once all items are
added, stir to suspend the debris. Then pour the contents into large clear cups.
Is the water drinkable?
Should farmers use the water to grow food?
Should people swim in the water?
Should people eat fish that lived in the water?
Distribute 5 medium cups and 2 bottles. Each group will prepare 5 different filtering methods.
1. Place a cotton pad over the top of bottle and secure with a rubber band. Invert and place
over a medium cup.
2. Place a coffee filter over the top of the bottle and secure with a rubber band. Invert and
place over a medium cup.
3. Place a piece of netting over the top of a medium cup and secure with a rubber band.
Invert and place over a medium cup.
4. Place a tea strainer over the medium cup.
5. Hold a funnel over the medium cup.
Set aside some water for a last demonstration (without disturbing the water as the class conducts
the experiment). Pour the “polluted” water into 5 large cups. Give each group a filled large cup
and in turn will pour the contents from the large cup into 5 small cups. Mark the water level on
each small cup. Have each student slowly pour the water from the small cup into the
strainer/funnel/bottle. Then compare their filtered samples to the standards. Pour water back into
the small cup and mark the new water level.
Students will record observations on the datasheet noting the materials used, the debris
found in the filters, the appearance of the filtered watered, and a comparison to the standard.
Record conclusions.
Have the class decide the best process for filtering (Let water decant first, then strain, use coffee
filter, followed by adding a cotton pad)
DEMO: Show the class the reserved “polluted” water. Hopefully, some debris has settled.
Cover cut end of the bottle with a coffee filter. Secure with a rubber band, creating a small “dip”
for water to well up. Invert and set inside a large cup. Hold strainer over cut end of the bottle.
Carefully pour water into the strainer. Take contents of this 1st stage filtration and process again
using a 2nd bottle. This bottle should have a cotton pad secured with a rubber band over the neck
opening, then inverted into a medium cup. Pour the filtered water into the bottle. Some (or
most) of the coloration should disappear.
Should they drink the water now? NO! The water still must be purified either by
adding a chemical, boiling, or setting in the sun to kill the unseen bacteria.
RELATED INFORMATION
Water Pollution
Pollution in water comes from many sources, such as human and animal waste, industrial
discharge, agricultural discharge, and natural processes. Animal waste contributes bacteria that
might be harmful to human and animal health. Animal waste and agricultural discharge contain
nutrients, like nitrogen and phosphates, which encourage the growth of algae. Human waste,
agricultural discharge and natural processes increase organic matter. As they break down the
matter, bacteria use up the oxygen in the water. Most pollution makes the water cloudy and may
contain chemicals. Both the bacteria and chemicals harm living things.
Cleaning discharge from homes
Septic systems: Septic tanks take the water that flows out of the pipes of the house. The contents
of the water settle into three layers: scum which floats, sludge which sinks, and the middle water
layer. That water contains chemicals and bacteria. It flows to the drain field. Dirt and gravel
slowly filter the water..
Wastewater treatment plant: A wastewater treatment plant is necessary when people live more
densely and do not have room for large drain fields. It has several stages to treating the water.
The first stage is like the septic tank, letting solids sink and scum float. The second stage uses
bacteria to eat the organic matter and nutrients, and then the bacteria settle out. The third stage
uses chemicals to clean the water before it is discharged.
Cleaning water for human consumption
Water for human consumption usually comes from the cleanest freshwater source accessible.
(Areas with primarily salt water must either import water or install costly desalination plants.) To
make water suitable for human consumption, the first step is filtering out large debris. To reduce
the salt content, soda ash is added to precipitate some salts. The pH is adjusted. Suspended
particles are removed. The resulting particles may be filtered out or allowed to settle out.
Disinfection of the water is accomplished with the addition of chlorine or by UV radiation.
Fluoride is added to many municipal water systems for dental health. Many families purify their
water further using a household water filters containing carbon. Boiling water can kill bacteria.
Iodine tablets, used by campers, and chlorine disinfect water.
Wetlands
Wetlands act as natural water purifiers, improving the quality of water, as well as provide other
benefits such as floodwater storage, fish and wildlife habitat, aesthetics, and biological
productivity. Wetlands function like natural tubs or sponges, storing water and slowly releasing
it. This process slows the water’s momentum and erosive potential, reduces flood heights, and
allows for ground water recharge, which contributes to base flow to surface water systems during
dry periods. After being slowed by a wetland, water moves around plants, allowing the
suspended sediment to drop out and settle to the wetland floor. Nutrients from fertilizer
application, manure, leaking septic tanks, and municipal sewage that are dissolved in the water
are often absorbed by plant roots and microorganisms in the soil. Other pollutants stick to soil
particles. In many cases, this filtration process removes much of the water’s nutrient and
pollutant load by the time it leaves a wetland.
Filtering methods work
Should you use carbon or sand? IT DEPENDS. Carbon granules are rough, having many small
crevices that can bind small molecules like food coloring. Sand is relatively smooth, so it mostly
removes large particles such as dirt.