Water Quality and Water Treatment— Teacher's Notes
Focus question
What are the key processes in treating polluted water?
Tools and materials
- Six 2-L transparent plastic bottles
- Clear packing tape
- Scissors or other cutting tool
- Water
- Vanilla flavoring
- Two “pinches” of soil
- Cooking oil
- Food coloring
- Two small sticks for stirring
- Silt, clay, or very fine sand
- Masking tape
- Permanent marker
- Two coffee filters
- Two rubber bands
- Clean sand
- Clean small gravel
- Alum (potassium aluminum sulfate)—available as a cooking spice
- Notebook
- Hydrogen peroxide (optional)
Note: You may want to wear safety goggles when handling the liquids for this activity.
Main ideas and background information
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The quality of a water supply is affected by the land area over which the water flows and the subsurface material through which the water flows.
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Both surface water and groundwater can become polluted by impurities.
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Surface water generally contains a greater variety of impurities, from a greater variety of sources. Polluted groundwater may contain fewer kinds of impurities, but there may be a larger amount of each contaminant than in a typical surface water supply.
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The most common pollutants generally fall into one of two categories. Organic pollutants include sewage, livestock wastes, and disease-causing microorganisms. Nonorganic pollutants include nutrients in fertilizers, industrial and commercial chemicals, road salts, agricultural pesticides, acidic mining wastes, runoff from buildings and other structures, waste heat, and radioactive waste.
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The goal of water treatment is to produce water that is safe for drinking and does not have objectionable taste, smell, or appearance.
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Generally, water for consumption is treated in a water treatment plant. Wastewater (sewage) is treated at a wastewater or sewage treatment plant. The water treated in this activity is not intended for consumption.
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Water treatment involves a series of steps. The methods applied depend on a community’s local water source and treatment needs.
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Primary treatment involves settling and perhaps chlorinating. Secondary treatment has to do with filtering and oxidation by microorganisms, and it results in water of much better quality. In some places, tertiary treatment is used, with flocculation (the formation of larger lumps from smaller particles), disinfecting, and use of specific additives to remove undesirable excess compounds of iron, manganese, and so forth.
Procedural tips
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We recommend the use of safety goggles for any activity in which students use liquids.
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In steps 5 through 7, students construct their filtering systems. Tamp down the sand gently but firmly. It will settle a bit more when the water flows through. If you cannot find clean sand and gravel, then use what you have and clean the filters by running water through them until it comes out clear. Cleaning time varies from a few minutes to several hours, depending on the condition of your sand and gravel
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In step 8, students add alum to the water in container 1. Make sure that they stir the water thoroughly for several minutes and then allow everything to settle. This is also a good opportunity to discuss the concept of the experimental sample (with the alum) and the control sample (without the alum).
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In step 9, caution the students that they should pour only the liquid into the filters, leaving any sediment in the original containers.
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In step 11, the optional hydrogen peroxide drop can represent a chemical treatment to kill harmful organisms. Sometimes it also makes the water sample a bit clearer.
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Be sure to review disposal procedures for the treated and untreated water after students have finished the activity.
Discussion
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Describe how water is purified in nature.
Natural water purification involves evaporation and condensation, which separate water from substances that are dissolved in it. Bacteria convert dissolved organic contaminants into simple and harmless compounds. Naturally occurring sand and gravel can filter out suspended material that makes water cloudy.
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What are some of the health hazards of domestic sewage?
The human wastes in sewage are not themselves especially harmful; however, the disease-causing microorganisms commonly found in sewage are hazardous to health. Many illnesses, such as cholera and typhoid, are caused by contact with sewage. Such illnesses are much less common in the developed world than in areas of the world where people are more exposed to untreated sewage. Coliform bacteria, a common type of bacteria that live in the intestinal tracts of all warm-blooded animals (including humans), are generally not harmful. Nevertheless, their presence in water supplies is commonly used as a signal of sewage contamination.
Assessment
Describe, in your own words, how pollutants can be removed from polluted water.
(Student description should include the role of chemical and physical treatments and information based on their activity observations.)
Extensions and further investigations
- For the activity, students treat simulated untreated water samples. If you feel it is appropriate, ask students to collect water samples from their local stream, pond, or lake. If students collect water samples, be sure they take note of the following safety precautions:
- Inform an adult of where they are going and their estimated return time.
- Go to the site in a team.
- Collect samples from the shore only—do not wade into bodies of water.
- Place samples in containers with secure and tight fitting lids.
- Label the samples.
- Rinse the outside of the containers with clean water.
- Wash and dry hands after collecting samples.
- Keep samples refrigerated and use them as soon as possible.
You may suggest that your students gather their water samples according to the following method outlined in the following SEED article: Water Quality: Procedure for Collecting Water Samples.
- Have students research how well their local water provider has maintained the water quality in their community.
- As water moves through soil, sediment, or bedrock, it dissolves some of the minerals. Water hardness reflects the concentration of dissolved solids—mainly calcium and magnesium—in the water. Groundwater tends to be harder than surface water, because it has had more time to be in contact with the solid materials. A disadvantage of hard water is that it reduces soapsuds. In can also leave hard, white deposits in tea kettles, on shower walls, and in water heaters and boilers. Water softeners reduce hardness by replacing calcium and magnesium ions with sodium ions. Have students line three funnels with filter paper. Ask them to place sand in one, put a water-softening chemical in another, and leave the third empty. Ask them to run an experiment with this design to find out whether the water-softening chemical or natural filtration by sand is a better method of softening water.
- Feces and urine from cats and dogs is a major source of water pollution in some urban and suburban areas. Ask students to determine the size of the cat and dog populations from their community’s authorities. Then, have students make assumptions about the average daily output of cats and dogs. Have them use this information to estimate the total weight of cat and dog feces and the volume of cat and dog urine deposited on the yards, sidewalks, streets, and other public areas of their community per year. Have students discuss the effects of this material on water quality in their community or in other areas surrounding their community.
- For further testing of the water in your area, students can use the water testing SEEDKIT.
Glossary / Vocabulary
- anaerobic bacteria
- bacteria that can live without oxygen.
- bacteria
- one-celled microorganisms that do not have a formal organization of their nuclear material.
- chlorine
- a substance used to kill harmful microorganisms in water.
- groundwater
- water contained in pore spaces in sediments and rocks beneath the Earth’s surface.
- hard water
- water that has a high concentration of calcium and magnesium ions.
- sludge
- the solid waste material that is separated from water in the treatment of wastewater.
- surface water
- liquid fresh water that resides temporarily on the Earth’s surface in the form of rivers and lakes.
- water pollution
- the addition of any substance that has a negative effect on water or the living things that depend on the water.
- water quality
- a measure of the suitability of water for a particular use based on selected physical, chemical, and biological characteristics.
- water treatment
- physical, biological, and chemical methods of removing impurities from water.
Adapted from: American Geological Institute. EarthComm: Project-Based Space and Earth Systems Science. 2nd ed. Armonk, NY: It’s About Time, 2012.
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This content has been re-published with permission from SEED. Copyright © 2025 Schlumberger Excellence in Education Development (SEED), Inc.