SummaryStudent teams practice water quality analysis through turbidity measurement and coliform bacteria counts. They use information about water treatment processes to design prototype small-scale water treatment systems and test the influent (incoming) and effluent (outgoing) water to assess how well their prototypes produce safe water to prevent water-borne illnesses.
A leading cause of childhood mortality in developing countries is water-borne illness. Health practitioners can usually treat these illnesses if they are caught in time, but engineers can prevent them from happening in the first place by designing and implementing effective water treatment systems to provide potable (i.e., suitable for drinking ) water to people around the world.
- A basic knowledge of water quality and ways to clean or treat water.
- An understanding that bacteria and viruses can be carried through a water supply and cause illnesses if the water is ingested.
(This knowledge can be obtained through the associated lesson, Test and Treat Before You Drink.)
After this activity, students should be able to:
- Describe measurement of water quality through turbidity and coliform bacterial counts.
- Design and build prototypes of small-scale systems to clean water.
- Evaluate water treatment methods and make recommendations for improvements to achieve better water quality.
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Each TeachEngineering lesson or activity is correlated to one or more K-12 science,
technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN),
a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics;
within type by subtype, then by grade, etc.
Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.
All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).
In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.
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Each group needs:
- Recycled/reusable materials (collected by students over the previous week). Material may include: empty plastic jars, plastic bottles, PVC piping, sponges, tubing, sand, gravel, plastic wrappers, etc.
- 1 clean container (able to hold at least 500 mL)
- 1 clean cup (able to hold at least 200 mL)
- 2 - 3M™ E. Coli/Coliform Petrifilm™ tests or other simple bacteria test (3M™ Petrifilm™ test strips can be ordered directly from the manufacturer by calling 1-800-328-1671 (item call #6404); $150 for 100 tests)
- 2 - 1 mL sterile syringes (no needle), for use with coliform tests
- 1 sheet of paper, to sketch design ideas
- Let's Clean Some Water! Data Worksheet
To share with the entire class:
- Secchi Tube Turbidity Meter (groups may make their own following the How to Make a Secchi Disk Turbidity Tube Manual, attached). Materials include:
- one long (~3 ft) piece of clear tubing with a cap for the end (e.g., a fluorescent tube light cover from a hardware store which comes with end caps)
- plastic container lid (e.g., from a yogurt or sour cream container)
- flexible water-tight glue (e.g., Gorilla glue)
- black permanent marker
- meter stick (for measuring)
- variety of tapes and glues
- cutting tools, such as scissors and utility knives
- dirty water collected from a nearby creek, river, pond, lake or other surface water source; enough for approximately 0.5 L per group
- a large, wide-mouth container with a lid for transporting/storing source water (to hold enough for approximately 0.5 L per group); may want to use a smaller clean container (such as a cut-open gallon jug) to scoop water.
- 3M™ Petrifilm™ Interpretation Guide
- How to Use a Secchi Disk Turbidity Tube Guide.
- bucket and bleach (to disinfect used test strips prior to disposal).
- latex or rubber gloves (for teacher use only; to use when bleaching test strips).
As a class, read through the following short play to introduce the topic of water quality. Choose three volunteers to act out the play for the class: Bongo Billy, Bongo Bertha, and Doctor Dan.
Scene 1: At the Bongo Family Home
Bongo Billy (age 4): Mom, I don't feel well. (Vomits on mom's shoes)
Bongo Billy's Mom, Bongo Bertha: Oh no, we should get you to the doctor right away!
Scene 2: At Doctor Dan's Office
Bongo Bertha: Doctor, little Billy has been sick all morning. What can we do?
Doctor Dan: Billy, what's wrong?
Bongo Billy: My stomach hurts, and I vomited four times this morning. Mom got mad because I threw up on her favorite shoes.
Doctor Dan: Hmm, have you been eating or drinking anything unusual lately?
Bongo Billy: I ate a worm yesterday! Mad Max gave me a nickel for it! But, that's not unusual, I often eat worms.
Bongo Bertha: We did start drinking river water three days ago. The well dries up in the dry season sometimes.
Doctor Dan: Hmm, we could have a case of a water-borne illness here; it might be E. coli.
Bongo Bertha: Oh my, what can we do?
Doctor Dan: I can give little Billy some medicine and then all we can do is wait to see if he survives. But, you will have to talk to an ENGINEER (superhero music plays in the background) to help you clean your water so the rest of your family doesn't get sick as well.
Bongo Bertha: Why an engineer?
Doctor Dan: Well, engineers prevent people from getting sick by designing ways to clean up contaminated water and make it safe to drink. Engineers are saving lives around the world!
Bongo Billy: That's awesome. Mom, I want to be an engineer when I grow up!
Your task, as an engineer, is to design a low-cost water treatment device to help keep Bongo Billy from getting sick again. (Teacher note: review the attached 5 Water Treatment factsheets in the Test and Treat Before You Drink lesson with the class and set up the design activity.)
As we have already learned, we know of several existing small-scale water treatment systems (illustrated in Figure 2), including BioSand Filters and Ceramic Filters, such as the Filtrón. For high turbidity water, pre-treatment methods, such as settling tanks that let large particles of debris settle out of the water and gravel filters, can be useful. Filter materials include items for removing large particles, such as screens, or fine filter materials for smaller particles, including gravel or cloth. Chemicals are also sometimes used for water disinfection (e.g., chlorine) and coagulation (e.g., alum).
One of the leading causes of childhood mortality in developing countries is water-borne illness (such as Bongo Billy's E. coli scare). New ways to clean water are being researched and designed by engineers all the time. Water treatment is site-specific, so each new location or water source poses unique problems and challenges for engineers.
Today, you are going to act as engineers, using what you have learned about physical and biological water treatment methods to design a model water treatment system for a natural source of water. Can you use what you have learned to design a system that will provide clean water for families such as Bongo Billy's?
bacteria: A one-celled microscopic organism (1-5 microns in diameter) that can, in some cases, cause disease.
coliform bacteria: Any of several bacilli, especially E. coli, found in the large intestine of humans and other animals, the presence of which in water is an indicator of the presence of pathogenic bacteria and viruses. (In the 3M test, the red dots are total coliform, which is not necessarily pathogenic and exists in naturally in soil; the blue dots are E.coli, which is an indication of fecal contamination.)
colony-forming units (cfu): A measure of living bacteria cells.
effluent: Water (fluid) coming out of a system after being treated.
influent: Water (fluid) going into a system (often dirty or unsafe to drink).
influent: Water (fluid) going into a system (often dirty or unsafe to drink).
pathogen: A disease-causing organism.
pathogen: A disease-causing organism.
Petrifilm: A test created by 3M to measure for coliform bacteria.
point-of-use: (as applies to water treatment) A point-of-use system disinfects water right at the location where you collect and use it.
potable: Fit or suitable for drinking. Potable water is safe to drink.
turbidity: A measure of the cloudiness or haziness of water (or other fluid) caused by individual particles (suspended solids) that are generally invisible to the naked eye. Measurements of turbidity are used to indicate water quality and filtration effectiveness.
virus: A microscopic particle (20-300 nm in diameter) that can infect the cells of a living organism.
Refer to the associated Test and Treat Before You Drink lesson and the 5 Water Treatment Fact Sheets for background information on small-scale water treatment systems. Encourage students to create their own system designs or use a combination of existing designs.
Before the Activity
- Collect dirty water from a nearby creek, river, pond, lake or other surface water source (dirt/mud/leaves, etc. can be added if the natural water is relatively clear and clean looking). Collect enough for approximately 0.5 L per group.
- If sand and/or gravel is extremely dirty, rinse with water to remove settled dirt and debris.
- Construct a simple Secchi turbidity tube, using instructions provided in the attached How to Make a Secchi Disk Turbidity Tube Manual.
- Create a space in the classroom where materials are available to the students.
- Identify a dark and warm space to put the microbioligical tests for their incubation period (35°C is ideal and will provide results in 24 hours, but room temperature will also work, although 48 hours should pass before results are read).
- Set out the large container of source water and another large container of tap water in the classroom (or just outside to prevent spills in the classroom).
- Make copies of the Let's Clean Some Water! Data Worksheet (1 per group), How to Use a Secchi Disk Turbidity Tube Instructions, How to Use 3M™ Petrifilm™ Instructions and the 3M™ Petrifilm™ Interpretation Guide.
- Divide the class into teams of 3-4 students. Hand out the Let's Clean Some Water! Data Worksheet (1 per group).
With the Students
Part 1: Design of Small-Scale Water Treatment Systems
Now that we know the quality of the water we need to treat, we can begin to design small-scale treatment systems to provide safe drinking water from our nearby source water.
- Have the students look at the water they will treat (the water previously collected by the teacher) so that they have an idea of the turbidity level with which they are dealing.
- Have the students look through the materials that are available for prototype construction.
- Following the engineering design process, brainstorm ideas for a water treatment system design (in groups of 2-3). Spend about 15 minutes brainstorming ideas.
- In their groups, ask them to discuss the pros and cons of all the ideas. (In the spirit of brainstorming, remind them to use constructive criticism at that no ideas are bad.) Ask each group to select the most promising concept to design for their prototype.
- On a piece of white paper, instruct students create a sketch of their design.
- Remind them to detail measurements and specify materials in their design.
- Have each group create a materials list for their design based on using recycled and reused materials when possible. (Remind them to include things like glue and sealant if they are necessary for their system.)
- Each group should discuss the final design and materials list with the teacher.
Part 2: Build and Test Prototype Water Treatment Systems
Now that you have finalized your design, it is time to build a prototype (model) of your design and see how well it works. See Figure 3 for inspiration.
- Each group gathers materials and beings construction. (Note: This should take approximately 2 hours to complete.)
- Once systems are ready to test, ask each group to collect 0.5 liters of water in a clean container from the dirty source water previously collected.
- Have each group pour 400 mL of the source water through their system and collect at least 200 mL of the effluent (outlet) water in a clean container. (Note: Be sure they SAVE the remaining 100 mL of source water and the 200 mL of effluent water for testing.)
- Test the influent and effluent water for coliforms and turbidity following the How to Use a Secchi Disk Turbidity Tube Instructions and How to Use 3M™ Petrifilm™ Instructions.
- Record turbidity data in the Let's Clean Some Water! Data Worksheet.
Part 3: Results and Analysis of Water Treatment Systems
Wait two days before completing the next two steps.
- Read the results of the 3M® Petrifilm, and record on the Let's Clean Some Water! Data Worksheet based on the 3M™ Petrifilm™ Interpretation Guide. The blue dots are E. coli, and the red dots are other coliforms. (Note: The World Health Organization recommends having less than 1-3 total coliforms (blue and red dots combined) per mL and zero E. coli (blue dots)).
- Record coliform bacteria results on the Let's Clean Some Water! Data Worksheet.
Part 4: Communicating the Results
Now that you have tested your prototype water treatment system with the source water, you need to communicate your results to the class. Address the following questions in your reporting:
- How well did your design work?
- What data supports your design?
- In what conditions would your design be best utilized?
- What changes would you make to your design if you were to create a second prototype?
Choose one of the following ways to communicate the results (or the teacher may assign one way for the class to use):
- Write a brief 3-page report based on your design and results.
- Create a poster or flyer describing your water treatment design.
- Create a short PowerPoint® or oral presentation based on your prototype.
- The bacteria colonies that are grown with the 3M® Petrifilm (or similar test) can make you very sick! Disinfect the tests before disposal by placing them at the bottom of a bucket and pouring water and bleach over them. After a few hours, pour the bleach solution down the sink and dispose of the tests in the garbage. This process should be done by the teacher, wearing rubber or latex gloves!
- Supervise all handling of the samples; no one should lift the plastic covering once a water sample is in place, especially after the bacteria have had a chance to grow.
- The presence of chlorine will impact your test results (killing bacteria), so if you test the prototypes for leaks using tap water, make sure to let the systems dry completely so all the chlorine (present in tap water) will be gone by the time you run your coliform tests on the effluent water. Alternatively, you could check for leaks using source water (if you have enough) or set aside a bucket of tap water a day or two before testing, so the chlorine will be gone (most will degrade/volatize in about 24 hours) by the time you need the water to check for leaks.
- If the 3M test is difficult to read or shows results not discussed in the 3M® Petrifilm Interpretation Guide, contact 3M at 1-888-3MHELPS between 7am and 6pm Central time Monday - Friday. If you are using a different test, call the manufacturer for assistance.
Discussion Questions: Solicit, integrate and summarize student responses. Ask students to recall what they already know about water treatment and water quality. Can they describe any examples of how to treat contaminated water?
Know / Want to Know / Learn (KWL) Chart: Create a classroom KWL chart to help organize learning about small-scale water treatment systems. On the classroom board or a large sheet of paper, draw a chart with the title "Water Treatment Systems." Draw three columns titled, K, W and L:
- K - What do you Know about small-scale water treatment systems designed for low-cost and low-maintenance? What things will you need to keep in mind?
- W - What do you Want to know about water treatment systems?
- L - What did you Learn about water treatment systems?
During the activity introduction, as facts and questions emerge, fill out the K and W sections. Complete out the L section at the end of the activity.
Activity Embedded Assessment
Define the Problem: Have the class discuss the design challenge. What is the problem they are trying to solve? After they have completed Part 1 with the source water, ask if the class wants to develop any performance standards as an additional project challenge, such as specific turbidity or bacteria counts that they would strive to meet. How does the maximum allowable concentration you choose for your system relate to the safety of the people using the filtration system? In other words, does setting a high allowable concentration correspond to a safer or less safe system?
Worksheet: Have students record measurements on their Let's Clean Some Water! Data Worksheet. After students have finished their worksheets, have them discuss the results in their groups and determine if the data is what they expected. Why or why not? How do you expect the performance of your system to change as you use if repeatedly? What does the change in performance say about the reliability of your system?
KWL Chart Continued: Fill out the L section of the KWL chart started at the beginning of the activity.
Communicating Their Ideas: Have student teams present their designs to the rest of the class using reports, posters, flyers, or PowerPoint®/oral presentations. Require each team to describe their models, their data, and what improvements they would make to their water treatment system if they were to re-design it.
Journal Reflection: Ask students to each write a paragraph in their science journal or on a sheet of paper to explain how the development of small-scale water treatment systems could impact the environment and society. What are some economic impacts of introducing small-scale water treatment systems into developing communities? What are some of the social or cultural implications of introducing a new technology to a community? For instance, if community members are unfamiliar with the concept of filtration, do you expect any hesitation in adopting or using a sand filtration device?
Design Iteration: If time permits, allow students to create a second iteration of their prototypes to see if they can improve the water quality of the effluent water. (Note: this will require more bacteria tests.)
Design Requirements: Give the students additional design requirements based on climate and weather of a specific community. For example, how might their water treatment system design need to be modified to consider hot-dry or wet-colder climates?
Local Capacity Building: A large part of engineering for developing communities involves training. Now that students have developed their simple water treatment systems for small communities, how would they train communities on how to use the systems? What types of maintenance might need to be provided by the people in these communities? Have students create training documents to leave with their communities.
3M Microbiology Worldwide. 3M. Accessed June 26, 2012. http://solutions.3m.com/wps/portal/3M/en_WW/microbiology-worldwide/home/
ContributorsChristie Chatterley; Malinda Schaefer Zarske; Janet Yowell; Denise W. Carlson
Copyright© 2006 by Regents of the University of Colorado.
Supporting ProgramIntegrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder
The contents of these digital library curricula were developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.
Last modified: August 10, 2017