This lesson provides an introduction to the treatment of drinking water to remove harmful or distasteful substances. Topics include the history of treatment and a brief listing of treatment processes. Students can examine a selection of online resources for more detailed information on modern treatment methods and potential contaminants. The lesson includes an activity in which they construct a model treatment plant and treat water that they have 'contaminated' themselves in order to observe firsthand the steps involved in purifying water for human consumption. Educational levels: Undergraduate lower division, High school

Matt Laposata

English

Digital Library for Earth System Education

 
Drinking Water Treatment 
 
Table of Contents: 
History of Water Treatment 
Drinking Water Treatment Process 
Activity: Simulated Drinking Water Treatment Plant 
Activity: Constructing the Filtering Apparatus 
 
History of Water Treatment  
 
Water has always played a prominent role in human 
civilization.  When people first began settling in one place and 
growing crops for sustenance, it was invariably near water 
sources like rivers, lakes, or groundwater springs.  Water was 
needed for drinking, preparing food, bathing, cleaning, 
irrigating crops, and a variety of other tasks, so it was 
important to have ready access to this resource.  The water 
sources used for supplying water were not always clean 
however, and treating drinking water to improve smell, taste, 
clarity, or to remove disease-causing pathogens has occurred 
in one form or another throughout recorded history.  Begin by 
reviewing the history of drinking water treatment with the  
document below from the U.S. EPA. 
 
 
The History of Drinking Water Treatment (PDF) (376 KB) 
Water treatment over time, summary of modern treatment methods 
United States Environmental Protection Agency 
http://www.epa.gov/safewater/consumer/hist.pdf 
 
 
Drinking Water Treatment Process 
 
Now that you are familiar with drinking water treatment, let's examine modern methods in 
greater detail.  In general, the treatment of drinking water by municipal water systems involves a 
few key steps:   
 
Aeration: The water is mixed to liberate dissolved gases and to suspended 
particles in the water column. 
 
Flocculation: The materials and particles present in drinking water (clay, organic 
material, metals, microorganisms) are often quite small and so will not 
settle out from the water column without assistance.  To help the settling 
process along, "coagulating" compounds are added to the water, and 
suspended particles "stick" to these compounds and create large and 
heavy clumps of material. 
 
Sedimentation: The water is left undisturbed to allow the heavy clumps of particles and 
coagulants to settle out.  
 
Filtration: The water is run through a series of filters which trap and remove 
particles still remaining in the water column.  Typically, beds of sand or 
charcoal are used to accomplish this task.   
 
Disinfection: The water, now largely free of particles and microorganisms, is treated to 
destroy any remaining disease-causing pathogens.  This is commonly 
done with chlorination (the same process used to eliminate pathogens in 
swimming pools), ozone, or ultraviolet radiation.  The water is now safe to 
drink and is sent to pumping stations for distribution to homes and 
businesses. 
 
Examine in detail the process of drinking water treatment and its relationship to human health 
with the resources below.  Once your review of this material is complete, proceed to the Activity.  
 
 
Drinking Water Treatment (PDF) (481 KB) 
A detailed examination of municipal drinking water treatment methods 
United States Environmental Protection Agency 
http://www.epa.gov/safewater/faq/treatment.pdf 
 
Drinking Water and Health: What You Need to Know! (PDF) (996 KB) 
Overview of potential contaminants in drinking water and related health effects 
United States Environmental Protection Agency 
http://www.epa.gov/safewater/dwh/dw-health.pdf 
 
 
Activity: Simulated Drinking Water Treatment Plant 
 
In this activity we’ll be treating "contaminated" water to observe firsthand the steps involved in 
purifying water for human consumption.  The activity will use everyday items to carry out the 
steps in drinking water treatment and you will record changes in the water’s properties as the 
process progresses.  The basic version of this exercise has you record the appearance and 
odor of untreated water as it moves through the various steps.  In some situations, depending 
on available equipment and personnel, you may also be able to measure turbidity.  Turbidity 
describes the clarity or “muddiness” of a water sample and is measured by examining the 
transmission of light through a water sample.  Turbidity is a particularly useful measure of water 
quality for this exercise, as it enables one to quantitatively track changes in the water sample as 
it moves through the treatment process.  Check with your lab instructor to see if turbidity 
measurements will be taken when you perform the exercise.  Directions for measuring turbidity, 
if applicable, will be provided by your lab instructor. 
 
This exercise is a modified version of the Water Filtration exercise from EPA's Environmental 
Education materials, and can be found with other exercises at 
http://www.epa.gov/safewater/kids/grades_4-8_water_filtration.html .   
 
 
Activity: Constructing the Filtering Apparatus  
The activity requires the construction of an apparatus for filtering the water sample.  Directions 
for constructing the apparatus and a complete list of materials are provided below.   
 
(1.) Obtain a plastic two-liter soda bottle with the bottom removed.   
(2.) Secure a coffee filter to the neck of the bottle with a rubber band. 
(3.) Turn the bottle upside down and secure it in place as described by your instructor. 
(4.) Gently add 400 ml of pebbles to the bottle.  Make sure the pebbles do not puncture the coffee filter. 
(5.) Gently add 800 ml of coarse sand on top of the pebbles.  Avoid shaking the bottle whenever possible.  
(6.) Gently add 800 ml of fine sand on top of the coarse sand.  Again, avoid shaking. 
(7.) Place a clean 500 ml beaker beneath the inverted neck of the bottle to collect the water from the apparatus. 
(8.) 
Clean the sand and pebbles by slowly pouring 5 liters of clean tap water (in 400 ml 
increments to avoid overflowing the beaker) through the apparatus.  Take steps to 
minimize the disturbance to the uppermost sand layer as you pour. 
(9.) 
Once the flushing of the filtering apparatus is complete, thoroughly rinse the collection 
beaker with tap water and return it to its place beneath the bottle.  Your apparatus is 
now complete and ready for use. 
 
  
Filtering Apparatus Diagram: 
(http://www.epa.gov/safewater/kids/filter.pdf) 
 
 
 
 
 
Materials: 
To view the original exercise’s materials and procedures, visit the EPA’s Water Education page 
at http://www.epa.gov/safewater/kids/grades_4-8_water_filtration.html .   
 
For each station, the following materials are required: 
1.5 L of “contaminated water” (batch prepare as 2.5 cups of dirt to 5 L of tap water) 
1 two-liter plastic soda bottle + cap, with bottom removed 
2 two-liter plastic soda bottles with top (cap through base of neck) removed 
20 grams alum (potassium aluminum sulfate), approximately 2 tablespoons 
800 ml fine sand 
800 ml coarse sand 
400 ml small pebbles 
500 ml (or larger) beaker 
1 coffee filter 
1 rubber band 
1 tablespoon for alum 
1 stopwatch (clock in room may substitute) 
 
 
 ESA 21: Environmental Science Activities 
Activity Sheet 
Drinking Water Treatment
 
Name: 
 
Instructor: 
 
Activity: Simulated Drinking Water Treatment Plant 
 
[WARNING]: The water used in the experiment is not suitable for drinking at any stage in 
treatment.  Hence, do not consume the water under any circumstances. 
 
Begin by familiarizing yourself with the lab procedures.  It is important that you know the steps 
well as mistakes may cause you to begin anew in the process.  If you are able to record turbidity 
measurements, obtain these measurements and  
 
 
Contaminated Water 
Cap and shake the container of contaminated water, and pour 1.5 L into one of the empty two-
liter bottles.  Describe the appearance and odor (and turbidity, if appropriate) of the water.   
 
Appearance: 
 
 
 
Odor: 
 
 
 
Turbidity: 
 
 
 
 
 
Step 1: Aeration 
Cap the two liter bottle and aerate the water by shaking it vigorously for 30 seconds.  Pour the 
water into one of the cut-off two liter bottles, and then pour the water back and forth between the 
cut-off two-liter bottles five times.  Once you are done, describe the appearance and odor (and 
turbidity, if appropriate) of the water.   
 
Appearance: 
 
 
 
Odor: 
 
 
 
Turbidity: 
 
 
 
 
Step 2: Coagulation 
The water should be in one of the cut-off two-liter bottles.  Add 20 grams of alum crystals to the 
container and stir gently for 5 minutes.  The alum will act as a coagulant and bind with the 
particles suspended in the water.  Describe the what happens to the appearance of the water 
during the 5 minutes. 
 
Appearance: 
 
 
 
 
 
Step 3: Sedimentation 
Leave the container undisturbed for 20 minutes, and record observations of the water's 
appearance (and take turbidity readings, if appropriate) at 5 minute intervals.   
 
Time (min.) Appearance Turbidity 
 
5 
 
  
 
10 
 
  
 
15 
 
  
 
20 
 
  
 
 
Step 4: Filtration 
Construct the filter apparatus as directed.  Carefully (and we mean carefully) and slowly (and we 
mean slowly) pour off the top two-thirds of the water in the container into a clean beaker.  It is 
important that you do not disturb the sediment when pouring, so take a great deal of care during 
this step.  Allow the water to settle, and then pour 400 ml of water from the beaker into the filter 
apparatus.  The water will percolate through the sand and pebbles and collect in the beaker 
beneath the apparatus.  Describe the appearance and odor (and turbidity, if appropriate) of the 
water after it has been filtered.  Pour the remaining water and sediment in the two-liter bottle 
back into the container of contaminated water.   
 
Appearance: 
 
 
 
Odor: 
 
 
 
Turbidity: 
 
 
 
Step 5: Disinfection 
The final step in the process, the elimination of any remaining microorganisms, will not be done 
in this exercise.  This is normally an important step in the process, but as the water is not to be 
consumed and disinfection methods can be dangerous outside of controlled conditions, this step 
will not done in this exercise. 
 
Analyzing Results: 
Create a graph that displays the observed changes in the quality of the water throughout the 
treatment process.  If you measured turbidity, graph the turbidity measurements versus 
treatment step.  If you did not measure turbidity, assign a scale to your appearance and/or odor 
observations (e.g., score odor on scale from 1 - 5, with 1 = very unpleasant odor and 5 = no 
discernable odor) and graph the scale values versus treatment step.   Create your graph in the 
space below.  
 
 


Drinking Water Treatment

http://esa21.kennesaw.edu/activities/drink-water-trt/drink-water-trt.pdf

Drinking Water Treatment

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