Hands-on Activity Gravity-Fed Water System for Developing Communities

Learning Objectives

After this activity, students should be able to:

• Define water poverty and relate the concept to global issues and the difficulty in providing sustainable solutions.
• Relate the general physics and fluid mechanic theory and principles that allow water to flow by gravity through pipe systems.
• Design and optimize a working gravity-fed water system based on constraints.

Educational Standards

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.

NGSS: Next Generation Science Standards - Science

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

For introductory teacher presentation:

• Gravity-Fed Water Systems Presentation (a PowerPoint® file)
• computer and LCD projector to show a PowerPoint presentation
• drill with ½" bit to start holes in tubs
• utility or Exacto® knife to further widen holes (as an alternative, ask the hardware store where you buy the tubs to drill the holes for you; ensure you have the pipe adapters to illustrate and clearly explain the layout of the holes)

Each group needs:

• access to water or, if necessary, a 5-gallon bucket filled with water
• safety glasses/goggles, one per student
• Gravity-Fed System Design Worksheet, one per student
• turbidity chart (to measure cloudiness), on the last slide of the presentation
• 2 calculators, for two students to check calculations
• 2 6-ft long 0.25" or 0.5" clear polymer tubing (or 1 of each; available at hardware stores)
• 1 3-ft long 0.5" clear polymer tubing to represent the tap (available at hardware stores)
• 5 0.25-in and 5 0.5-in threaded hose barbs (thread on one end and barbed on the other), with o-ring that goes over the threaded section, along with a metal or plastic nut that threads on to the threaded section (available at hardware stores)
• 3 clear 5-gallon tubs, holes drilled for the following; for more information, see the Procedures section and Figure 1 (tubs available at hardware/discount stores): pipe adaptors for exit of spring catchment basin or dam (tub 1), entrance and exit for sedimentation tank (tub 2), entrance only for "community" tank (tub 3)
• 2 cups of dirt (sediment)
• 2 stopwatches to measure flow rate
• (5) 2' x 2' cardboard boxes, or larger cardboard boxes (to place tanks on)
• 1 clear plastic cup (end user) (note: this is the cup of water that students fill with tub 3 water to insinuate drinking)

To share with the entire class:

• 12 6-ft long 0.25" clear polymer tubing (available at hardware stores)
• 12 6-ft long 0.5" clear polymer tubing (available at hardware stores)
• 3 hoses connected to classroom taps to fill tub 1 (dam/catchment)
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Worksheets and Attachments

Introduction/Motivation

Have you ever missed school because you were sick with some kind of "stomach bug?" How much school did you miss? A doctor might tell you to stay hydrated by drinking plenty of water. But, imagine if it was the water that kept making you sick, and if drinking more water kept you in a cycle of sickness! What if you were too sick to return to school? What if your family could not afford the doctor bills? This is an example of what we call "water poverty." In fact, any source of water that is too dirty, too far away, or too expensive is a form of water poverty. The cycle of water poverty is experienced by more than 800 million people around the world.

The problem of water poverty has led to an uprising of engineering development projects to aid in the building of water infrastructure to provide clean water to poor and rural communities in developing countries. The typical water distribution treatment system installed in a community usually falls either within centralized systems (wells, gravity-fed systems) or point-of-use systems (POU), which is the treatment of water at the household level, either by filtration or chemical disinfection. Gravity-fed water systems—often a high initial investment due to the cost of pipes, and often a lengthy distance from the clean water source to the community—typically have a longer lifespan due to no moving parts (pumps) or energy requirements (electricity, gas, diesel). These types of water systems, therefore, are more sustainable. Since piped systems can only create a water flow by gravity from a higher to lower elevation, gravity-fed systems only work if the water source is significantly higher in elevation than the community being served.

When engineers design gravity-fed water systems, they consider many constraints (requirements and limitations) on system performance:

• Water Source Quality and Quantity: If the source water is not clean, it cannot be used. If the water quantity changes throughout the day and does not meet the community water demand, it will not work.
• Topography (how the surrounding land is shaped): The topography must allow for water to flow at all locations along the pipe through pressure differentials that result from water flowing from higher to lower elevations.
• System Demand: This is a function of the number of people using the system and the amount of water allocated to each person.
• Frictional Loss: Just like with a system that has moving parts, friction can occur in water systems as the water flows through the pipes and results in loss of pressure along the pipe, which can prevent flow altogether.
• Pipe Size and Length: Engineers design pipe size based on how much water is needed by the community and how much friction will occur through the pipes.

In addition to considering constraints before designing and building water systems, engineers seek to discover the turbidity of water before deciding to use it as a water source. Is it clean enough? Turbidity is the "cloudiness" or "darkness" of drinking water, used as a metric for contamination, whereas a higher NTU (or, Nephelometric Turbidity Units), would mean a higher turbidity, and thereby higher contamination. NTU goes up as the water becomes cloudier and/or darker. Clearly, water with high turbidity would have a higher chance for contamination

Procedure

Before the Activity

• Gather materials. Make sure you have twelve (12) 6-ft sections of both 0.25" and 0.5" polymer tubing, twenty (20) 0.25" and twenty (20) 0.5" threaded hose barbs each with o-ring and nuts, twelve (12) 5-gallon clear tubs, six (6) 3-ft sections of 0.5" polymer tubing, a bin of dirt, ten (10) clear plastic cups, twenty (20) cardboard boxes.
• Drill holes in the ends of each tub, as illustrated in Figure 1:

Tub 1: Dam or Spring Box, with two (2) exit holes positioned on the bottom of the tub, one for the 0.25" hose barb (left) and the other for the 0.5" hose barb (right).

Tub 2: Sedimentation Box, with two (2) entrance and two (2) exit holes positioned at the top of the tub, both sides to accommodate 0.25" hose barb (left) and the other for the 0.5" hose barb (right).

Tub 3: Distribution Tank, with two (2) entrance and two (2) exit holes positioned at the top and bottom of the tub, respectively; both sides to accommodate one 0.25" hose barb (left) and the other for the 0.5" hose barb (right).

• Make copies of the Gravity-Fed System Design Worksheet, one per student.
• Display the Turbidity Chart (last slide in the presentation file) during the activity.
• Have the Gravity-Fed Water System Presentation (PowerPoint file) ready to show the class.
• Determine tub placement to allow for maximum flow; that is, Tub 1 on table, Tub 2 on chair next to table, Tub 3 on the floor.

With the Students

Day 1: Topic Introduction and Brainstorming (Assessment)

1. Do the Pre-Activity Assessment with students (as described in the Assessment section). This connects with the beginning of the presentation, in which students learn a few important statistics regarding water poverty and some of the science behind waterborne disease.
2. Show students the presentation; particularly direct their attention to the seriousness of water poverty, what causes waterborne illness, and how this problem truly needs a solution. Introduce the turbidity chart on the last slide.
3. Provide students with the worksheets and briefly discuss the design activity. Provide an overview of what the activity entails: preliminary design, presentation to class, testing water system designs and changing. With the design, the goal is to have the highest flow (volume per time; that is, gallons per second), while having the greatest turbidity change.

Day 2: Preliminary Designing and Prototype Building

1. Start class by reiterating the design activity (outlined in the worksheet).
2. Divide the class into groups of six students each.
3. Instruct them on how they can draw their preliminary designs and create a desired materials list (pipe sizes, tub elevations, pipe locations, etc.).
4. Inform students that they can change the following parameters: tank elevations, tube diameters (sizes), and tube locations. Remind them how changing these parameters can affect the flow, where again, the goal of the activity is to have the water go from the top tank to the bottom tank the fastest, while changing the turbidity of the water as much as possible.
5. Have students turn in their preliminary design and rationale (drawing and parts list) for approval.
6. Leave enough time for the Activity Embedded Assessment (discussed in the Assessment section), which includes group presentations.

Day 3: Building and Testing the Prototype

1. Demonstrate an example connecting the water system to tubs, and how water flows between tubs, by adding 1-gallon of water to the top tub (do not be partial to your design, just show the general design concept). Show exactly how you connect the tubes to the tub.
2. Have stations set up for groups with boxes, tubes, tubs, dirt and cups. Attach hoses to classroom facets. If no faucet or convenient access to a faucet is available, fill up six (6) 5-gallon buckets and use those to fill Tub 1.
3. Give groups time to build their gravity-fed water systems, guiding them through the steps or in helping to solve any challenges they encounter (see Figure 2).
4. Once systems are fully put together, have teams test their designs without dirt to ensure water is flowing from tub to tub. This entails filling the top tub with about 1-gallon of water, and watching the water flow from top tub to bottom tub (Tubs 1 – 3) if working properly. Please take notice of any water leaking from improperly attached tubes—have a mop and bucket available for cleanup.

   

5. Then place the full 2 cups of dirt in Tub 1; add 2 gallons of water; mix well while the system is beginning to flow. Have students refer to the turbidity chart to make note of how the water quality looks.
6. Have students record the time it takes for water to transfer from Tub 1 into Tub 3, and note any complications within the tubs with regard to filling (that is, overflowing of one tub, one tub being emptied, etc.) on their worksheets.
7. Once the water has stopped flowing, instruct students to declare the turbidity of water in Tub 3 (to ascertain how sedimentation affected turbidity), using Figure 3 for reference.
8. Let students change their designs (see worksheet), and indicate their changes with their rationale behind it.
9. Test the revised design, and make note of system performance, as indicated on the worksheet.
10. Close with a 10-minute discussion on what students learned (see Post-Activity Assessment in the Assessment section). Be sure to focus on explicitly identifying which parameters caused the flow and sediment removal to be the most effective. Overall, ask students what they learned about the process of designing and building gravity-fed water systems.

    

Vocabulary/Definitions

bacteria: Microscopic single-celled organisms; may be beneficial or highly infectious to humans; in the case of waterborne illness, a harmful virus is E-coli.

diurnal water cycle: The amount of water available in a stream over the year.

flow: The amount of water flowing per unit time (volume/time) (cu. ft/s).

fluid density: The density of a fluid (water) which is mass (kg)/volume (cu.ft).

gravitational potential energy: The energy potential that exists due to relative vertical position.

kinetic energy: The energy of motion.

parasite: An organism (microscopic and macroscopic) that lives on a persons' nutrients; in the case of waterborne illness, common parasites are Guinea Worm, Cryptosporidiosis, and Giardiasis.

pore size: The size of the holes in a water filter; typically sized to let water pass through, while being too small to allow harmful organisms to pass as well.

pressure: A weight per area (lbs/sq.in).

roughness coefficient: Coefficients given to denote roughness (friction) in pipes.

sedimentation: The settling out of sediments by gravity in a water system.

virus: A very small organism that causes a disease to spread throughout the body; an example of a virus is Rotovirus (the stomach flu), or influenza.

water demand: The amount of water needed per person per day, summing by number of people in a community.

Assessment

Pre-Activity Assessment – Before Activity Presentations

What Is Water Poverty? Class Discussion: Ask the class: "What does water poverty mean to you?" Ask students to raise their hands to answer the question; select a few students to share their ideas. (Answer: water poverty is the condition of not having access to sufficient and/or clean water to meet one's basic needs.)

Then ask: "What do you think are some causes of water poverty?" Have students raise their hands to share their ideas. Write student ideas on the classroom board. (Possible answers are listed below.)

• Economic (Notice that water poverty does not exist in the U.S. "Why is that?")
• Political (Ask, "Why doesn't the government provide people with clean water?")
• Technical (Maybe the technology needed to provide clean water does not exist for a population. "Why not?")
• Environmental (Fact: In some areas of the world, no water may be available.)

Gravity-Fed Systems Brainstorming: Review brainstorming guidelines with students (no idea is silly, all ideas should be heard, withhold judgment, write down all ideas, etc.). In small groups, have students brainstorm what they think is meant by "gravity-fed water systems." Choose one person from each group to share his/her group's ideas.

Activity Embedded Assessment

Student-Generated Design Presentation: After groups have designed their water systems, direct them to prepare very short (verbal) presentations to discuss their general design ideas with the class. Ask each group the following questions to gauge their understanding of gravity-fed systems:

• How does your design ensure maximum flow, flow equalization in tanks, and maximum sediment removal?
• What are possible complications that might arise?
• How might you change the design if these complications take place?

Post-Activity Assessment

Project Reflections: After testing their systems, put the following questions on the classroom board and give students time to write answers based on their wrap-up thoughts from the activity.

• What design considerations seemed to work best— not just in your group but across all groups?
• What problems did it seem like all groups had, including yours?
• What do you think is the hardest part about gravity-fed water system design?
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Safety Issues

• Have students wear eye protection throughout the activity. Even though the lab only deals with water, expect spills, spraying and splashing of the dirty water. Remind students that wearing eye protection is a necessary habit when dealing with liquids in any lab setting.

Troubleshooting Tips

• Experiment with the water system building in advance to ensure the materials all work together and that no leaks occur and the tubes fit.
• To avoid delays, have ready a model prototype to show at the beginning of Day 2.
• During student testing, quickly take notice of water leaking from incorrectly attached tubes; have a mop and bucket available for cleanup.

Activity Scaling

• For lower grades, have students spend less time with the design process and presentations, and more time building and testing their prototypes.
• For upper grades, have students take more time with the design process, focusing more on the concepts articulated in the presentations and gathered from intuition and theories presented by their classmates in the pre-build discussion on Day 2.
• For upper grades, incorporate a final design stage in which each student draws his/her final designs based on what s/he learned from the testing and presentations. Have them turn in their designs for grading or participation marks.

Copyright

Contributors

Supporting Program

Acknowledgements

This digital library content was developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. DGE 0338326. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.