Lesson 4: Water Treatment Practices

Grade 5-9 (health, science and social studies)
Grade 10-12 (health, science and social studies)

Topic: Common methods of treating water.

Time: 60 minutes

Space Requirement: Regular classroom

Methodology: Group work, scenario resolution

Materials: Fact sheets, scenario sheets, overhead of arsenic test

Objectives: The students will look at five water treatment processes and identify the effectiveness, practicality and applicability of each. Students will also examine other methods that influence water quality and treatment methods, including education, funding, rights and treaty rights.

For the Teacher: The goal for this lesson is to give the students a chance to look at the three most common water treatment processes (coagulation, filtration and chlorination), as well as newer methods that will improve water treatment. They should begin to understand the difficulty in producing safe drinking water, especially from poor source waters.

This should lead to a realization of the importance of a multi-barrier approach. Many people rely on testing the treated water for contaminants. But this is not an effective means of producing safe drinking water, for two reasons: First, by the time a contaminant is discovered, the water will be in the pipes and on the way to homes in the community (thus, requiring a Boil Water Advisory). Secondly, the concentration of contaminants in treated water is continually changing, and it is much more effective to use treatment processes that WILL remove contaminants than to continually check to see IF they have been removed.

Fact sheets for each treatment method are available through the Safe Drinking Water Foundation website (www.safewater.org) and from the links below. It is very important that the teacher read the fact sheets prior to class.


  1. Assign each student one of the following aspects of treating water and provide them with the corresponding handout and questions. The handouts are found below.
    a. Conventional Treatment: Coagulation and Filtration
    b. Biological Treatment
    c. Ultrafiltration, Nanofiltration and Reverse Osmosis
    d. Disinfection: Chlorination and UV Irradiation
    e. Boil Water Advisories
  2. The students should use the first 15 minutes to read the handout and answer the questions relating to their treatment method. (15 min)
  3. Group the students according to their water treatment method. The students should then discuss the method and questions with their group and elaborate upon answers as needed. (10 min)
  4. Move the students into new groups so that each group has at least one representative for each water treatment method. Present the scenario (see below) to the class and have the groups develop an answer to the problem. Each student should have a chance to speak about their water treatment method and as a group, they must hand in a plan for resolving the problem from the scenario. (15 min)
  5. As a class, discuss the scenario and the solutions that each group developed. Emphasize that treating water is a difficult task, because the water can contain a variety of contaminants, including bacteria, protozoa, viruses, dissolved substances and chemicals. Most of the treatment methods can effectively remove some types of contaminants, but they cannot remove others. This is why it is very important to have a multibarrier approach to treating water. Using a combination of effective treatment methods, we can be sure that the water that is produced is safe to drink. (5 min)
  6. Read through the “Filters for Families” fact sheet with the students. If possible, have the pictures from this fact sheet put onto overheads ahead of time, so that students can visualize the water situation in Nepal. This fact sheet illustrates how water treatment methods are adapted to effectively remove arsenic from the water.
  7. Ask the students where is the world they think arsenic poisoning occurs. As many will likely believe that arsenic poisoning would not occur in countries like Canada, show them the overhead of the water test, and point out the arsenic level that was found in the water (in Canada, the maximum allowable concentration is 0.010 milligrams per litre or parts per million). (1 min)
  8. Ask the students where they think this water sample was taken from. The water test was taken on a farm near Saskatoon, Saskatchewan. The water on this farm is supplied through a well. (1 min)
  9. Now ask them if the water is safe. If yes, is it safe for everyone? If no, what should be done about it? The government does not believe that the high level of arsenic poses a problem, because the water is used for the cattle on the farm. Ask the students if they see any problems with this rationale. (8 min)
    Answers should include: people eat the meat from the cows that drink the water; aquifers are connected deep within the earth, and may supply other people with drinking water, further down the aquifer.
  10. Write the journal question on the board for the students to answer in their water journals: “Does Canada have a drinking water problem? What can you do to improve drinking water in your home, school or community?” (5 min)

Evaluation: The groups should be evaluated on the practicality of their plan. Each plan should include more than one treatment option because each treatment has a weakness that another treatment method can address.

Resources: Follow the links for fact sheets to use for each treatment method:
- Conventional Treatment: Coagulation and Filtration
- Biological Water Treatment
- Ultrafiltration, Nanofiltration and Reverse Osmosis
- What is Chlorination?
- Filters for Families
The following resources and handouts are found below:
- Water Treatment Scenario (Elementary)
- Water Treatment Scenario (High School)
- Water Treatment Questions
- Water Treatment Questions Answer Key
- Arsenic Test

Extension Activity: The Safe Drinking Water Foundation has other educational programs that can be taught with this set of lessons. Operation Water Drop examines the chemical contaminants that can be found in water; this program is designed for a science class. Operation Water Flow explores the use of water and where it comes from; this program is designed for a Social studies and Math collaboration. Operation Water Spirit presents a First Nations perspective of water and water issues and is designed for a Native Studies or Social Studies class. Operation Water Health explores common health issues surrounding drinking water in Canada and around the world and is designed for a Health, Science and Social Studies collaboration. To access more information on these and other educational activities visit the Safe Drinking Water Foundation website at www.safewater.org.

Sources and Related Links:
- Groundwater – a SDWF fact sheet
- Human Rights – a SDWF fact sheet

Water Treatment Scenario (Elementary):

A community gets its drinking water from a nearby lake. After many years, the company responsible for emptying the septic tanks in the community has shut down and a new company from out of town now empties the septic tanks. It would cost the company more money to haul the waste to their plant so the company has been dumping their trucks in a pit near the lake.

Two months after the new company began to empty the septic tanks, people in the community became sick. The first people to get sick were the elderly and the children. Then others in the community became sick too. They all had similar symptoms including diarrhea, nausea and vomiting.

Your group represents a task force set up to find out what made the community sick, who is responsible for it and what can be done to fix the problem. You must hand in a written plan that outlines who is responsible, what the people are probably sick with, and what can be done to fix the problem. You should also include any decisions you make regarding the people who are responsible.

Water Treatment Scenario (High School):

A community has a baseball tournament that lasts a week. Teams from the surrounding area come to the community and either stay in the hotel, camp out or stay in RVs. To facilitate the increased numbers of people in the community, port-o-potties are set up around the campsite and ball diamonds. There are also hand-washing stations set up outside the facilities. The company that operates the port-o-potties hires extra workers to clean out the port-o-potties every night and restock the hand washing stations during the day. The new staff is swamped by the increased workload and decides to empty their septic trucks into the river (the drinking water source for the community), rather than into the proper disposal area, because the river is closer and they can get more work done in a shorter period.

As the ball tournament begins to wind down, people begin to get sick. At first, three kids get sick and are taken to hospital. Then more and more people become ill. Over the next week, the number of sick people rises and includes almost everyone who was at the ball tournament and most of the community. There are no deaths but the final count of people who became sick is over 1000.

Your group will act as a task force and include people from the health district, environmental experts, the water treatment plant manager, the mayor, the port-o-potty owner, and residents of the community. Your group must assess the situation and come up with a plan to identify the source of the outbreak, the treatment for the outbreak and the outcome of the outbreak. Your plan is to be submitted in writing at the end of the class.

Water Treatment Questions:

  1. There are several methods of water treatment. Which method did you look at?

  2. Describe how this method works to improve water quality. What does this method remove from the water?

  3. Can this method be used by itself to make healthy drinking water? Why or why not?

  4. Would you drink water that had been treated with only this method? Explain your answer and give reasons why or why not.


Water Treatment Questions Answer Key:

  1. There are several methods of water treatment. Which method did you look at?

    a. Conventional Treatment: Coagulation and Filtration
    b. Biological Filtration
    c. Membrane Filtration: Ultrafiltration, Nanofiltration and Reverse Osmosis
    d. Disinfection: Chlorination and UV Irradiation
    e. Boil Water Advisories

  2. Describe how this method works to improve water quality. What does this method remove from the water?

    a. Coagulation works by adding iron or aluminum to the water. These chemicals cause the dissolved and suspended particles to bind together. The bound particles (called floc) become heavier and fall out of the water. There are two main types of filtration: slow sand filtration (using bacteria to consume contaminants and allowing the water to pass through the fine sand filter) and rapid sand filtration (forcing the water though a sand filter). Slow sand filtration can remove nearly all contaminants from the water, but rapid sand filtration cannot remove small particles, such as viruses.
    b. Biological filtration works by using natural microbes to ingest the contaminants in the water and convert them to less harmful substances (like oxygen and carbon dioxide).
    c. Membrane filtration works by allowing only molecules smaller than the pore-size through the filter. Ultrafiltration removes bacteria, protozoa, and some viruses. Nanofiltration removes these microbes, as well as most natural organic matter and some minerals (especially divalent ions which are responsible for hard water). Reverse osmosis removes turbidity, including microbes and virtually all dissolved substances. While reverse osmosis removes many harmful minerals, it also removes some healthy ones, such as calcium and magnesium.
    d. Conventional disinfection uses chlorine to inactivate microbes that are in the water. Chlorination can inactivate a large number of bacteria, viruses and protozoa, but it cannot inactivate Cryptosporidium. UV Irradiation uses sunlight to disinfect water. While this process was typically used for treating wastewater, it is a growing method for treating drinking water. After exposure to sunlight for several hours, the viruses and bacteria are inactivated.
    e. Boil Water Advisories are issued by the government in cases where coliforms such as E. coli are detected in the treated water or when there is a new system start up. Boiling the water inactivates the disease-causing microbes but does not remove any chemicals or other contaminants.
  3. Can this method be used by itself to make healthy drinking water? Why or why not?

    a. Coagulation and filtration should be supplemented with a form of disinfection, because some coliforms, bacteria and viruses may be too small to remove with this process.
    b. Biological Filtration is an effective treatment method. Because the process uses natural microorganisms to digest the contaminants in the water, it can produce clean water. While biological filtration should remove all contaminants from the water, it is still advisable to use a form of disinfection, to ensure that all harmful substances are removed from the water, and any bacteria that may remain do not have the opportunity to multiply.
    c. Ultrafiltration may not remove all viruses from the water, so it is advisable to use disinfection after filtering. Water that is treated using nanofiltration may not be free of dissolved compounds, so additional treatment will be necessary. Water that is treated using reverse osmosis is pure water.
    d. Disinfection should not be the primary water treatment method, because it may not remove all dissolved substances some of which can be hazardous. As well, when there is a high amount of dissolved matter in the water, significant amounts of chlorine must be added, because chlorine reacts with the dissolved matter before microbes can be inactivated.
    e. Boil Water Advisories serve to alert people that their drinking water may be unsafe. However, Boil Water Advisories can last for many years, and often do not address the real issues of water contamination and inadequate methods of treatment. Boiling water can remove bacteria and viruses, but it is insufficient to remove chemicals, such as arsenic, from the water.
  4. Would you drink water that had been treated with only this method? Explain your answer and give reasons why or why not.

    a. Coagulation and filtration: No, because there may be disease-causing microbes and chemicals still in the water. It should be disinfected after treatment using either chlorination or UV irradiation.
    b. Biological Filtration: Yes.
    c. Ultrafiltration, Nanofiltration and Reverse Osmosis: Yes, if it was treated by reverse osmosis.
    d. Disinfection: Chlorination and UV Irradiation: No, because there still could be contaminants in the water.
    e. Boil Water Advisories: Yes and no. Yes, because there would be no microbes left active after boiling. No, because there may be other contaminants (chemicals) still in the water.
SRC Analytical water test results