By Amy Gambrill, Washington, D.C.
Secondary science, social studies and current events classes
Two 45-minute class periods plus additional time for extension activities.
9 – 12
- Research where their local drinking water comes from.
- Explore pollution and other risks to drinking water sources.
- Investigate the relationship between water treatment and public health.
- Examine what happens when water goes down a toilet, down the drain, and into sewers.
- Understand drinking water and wastewater treatment processes.
- Become familiar with the laws that govern drinking water and wastewater treatment.
Roughly 70 percent of the earth’s surface is covered in water. Even though water seems to be everywhere, not all of it is suitable for use as drinking water. Of all the water on earth, only 3 percent is fresh water, with much of it frozen or under ground. And less than one percent of the water on earth can be used as drinking water. Before we drink it and before it is released back into surface waters (such as rivers and lakes), our water must go through a variety of treatment processes.
Over two class periods, you will be guiding your students through the basics of water treatment — both tap water treatment and sewage (or wastewater) treatment. To prepare for the lessons on the treatment process, the students will be researching where their drinking water comes from and where their wastewater goes once it goes down the drain for homework. After learning about their local water treatment and traditional tap water and sewage treatment processes, students will watch the NewsHour segment on water reuse in California. This will be a great opportunity for your students to make informed opinions about the subject. Encourage lively discussion about the topic. What is their reaction to it? What do they think about the water crisis in this country? Once they have learned about water treatment, there are many opportunities for extension, from legislation and public health to science labs and bottle vs. tap debates.
Talking about wastewater can be embarrassing for some students, but it will be important to define your terms so that they can talk without feeling strange about the topic. (See attached worksheet to familiarize your students with the technical terms associated with water treatment.)
Drinking Water Treatment Basics
The Safe Drinking Water Act requires that all drinking water go through a treatment process before it is sent to our taps.
Local water suppliers that use water from a local surface water (rivers, lakes, or reservoirs) must use a treatment process to take out any dirt particles, other organic matter (such as leaves and sticks), and contaminants. The suppliers add chemicals called coagulants so that this matter will form clumps and settle to the bottom of the tanks that store the water. Once the clumps settle, the water is put through a filter to remove any microscopic germs.
Water suppliers that use water from an underground source use a different process. Ground water is naturally filtered as it passes through the earth into underground reservoirs called aquifers. Water that comes from wells usually does not contain as much organic material as water from rivers and reservoirs.
The most common drinking water treatment is disinfection. Most water suppliers add chlorine or other disinfectants to kill bacteria and other germs. They may use other treatments to make the water clean and safe, depending on the quality of their source water.
Wastewater Treatment Basics
The Clean Water Act requires that states and municipalities regulate any discharges into surface water (such as rivers, lakes, wetlands, estuaries, and oceans).
Wastewater is used water–it is often called sewage. Wastewater is water that has been used in homes or by industries and businesses and disposed of via sewers that cannot be reused or discharged back into nature unless it is treated by a licensed wastewater facility. Wastewater can include substances (called suspended solids) such as human waste, food scraps, oils, soaps, and chemicals. In homes, wastewater is what goes “down the drain” from sinks, showers, bathtubs, toilets, washing machines, and dishwashers. Businesses and industries release large amounts of wastewater from their machinery, cooling processes, and other uses that also must be cleaned before being released back into surface water. After a rainstorm, the water (called storm runoffor storm water) that washes off roads, parking lots, driveways, and rooftops is considered wastewater because it can contain harmful substances that harm local surface waters.
The goal of wastewater treatment is to remove the suspended solids from wastewater so that it can be returned back to the environment safely. If these solids remain in the water, as they break down, they use up the oxygen in the water that supports the plants and animals living in the water.
Most wastewater treatment usually uses two to three steps:
Primary treatment removes 40-50 percent of the solids. Sanitary sewers carry wastewater from homes and businesses to the treatment plant. Bar screens let water pass through, but not trash or other large objects. The trash is collected and properly disposed of. A grit chamber, a large tank that slows down the flow of the water, allows sand, grit, and other heavy solids to settle at the bottom of the tank for removal.
Secondary treatment removes approximately 90 percent of the pollutants. A secondary sedimentation tank allows the microorganisms and solid wastes to form clumps and settle at the bottom. The water is then aerated.
Tertiary treatment completes the process. It can involve more filtration and nutrient removal. The wastewater is then treated with a disinfectant, such as chlorine, before it is discharged from the treatment plant. The disinfectant kills disease-causing organisms in the water. After treatment, the water can be safely returned to nearby waterways.
Guiding the First Lesson: Drinking Water
The day before you begin the lesson, have students research where their drinking water comes from. This can be found in a local water utility bill or online. Is your water from a local river, reservoir, well, or another source?
All animals and plants need water to live. We all depend on fresh, clean water every day to keep us healthy. We rely on our tap water to supply us with safe, clean water to drink. Other animals rely on rivers, lakes, bays, and the ocean. Where does our local water come from? Does anyone know the source of our drinking water? Do we all have the same source? Does anyone know how our water gets to our pipes? What do you think needs to happen to the water before it gets to our tap? Does anyone know the process that our water has to go through to be clean and safe for drinking? Have you ever filtered anything?
Let’s go over how water is treated before it can become safe drinking water. The process involves five main steps.
- Aeration adds air to the water, which add oxygen to the water and allows any gases to escape.
- Coagulation makes large particles coagulate into larger clumps.
- Sedimentation is a process which allows the clumps to drop to the bottom of water treatment tanks into settling beds that collect the particles.
- Filtration cleans the water.
- Disinfection kills bacteria and germs that may remain in the water.
Use background (above) to describe water filtration or demonstrate by making a filter to show how simple rocks, gravel, and sand can clean dirty water and highlight how disinfectant chemicals protect us from any remaining bacteria or germs.
Visit the EPA website for information on how to create your own filter.
For homework, have the students locate their watershed and major waterways or other sources of water in your area. Visit the EPA or the US Geological Survey online to learn the name of your local watershed. Have them identify where the local wastewater treatment plant is located and what communities it services. Can they find out where their used water ends up?
Guiding the Second Lesson: Waste Water (Sewage)
We have studied drinking water treatment. Now let’s discuss wastewater treatment. Does anyone know what “wastewater” is? Who produces it? What happens to it? Where does your used water go? Where is our local sewage treatment plant? Does it smell? Why?
Wastewater (or sewage) treatment usually happens in three steps. See above background or use this online diagram.
Watch the NewsHour segment, California County Turns Wastewater into Drinking Water. Note that 15 municipalities are currently using the water reuse process. Address some of the following issues:
- Now that we have learned about traditional drinking water and wastewater treatment, who can explain the water reuse process?
- What is the difference between traditional water treatment and the water reuse process?
- Discuss the pros and cons of water reuse?
- Given that most of the general public doesn’t know about water treatment as you do, what are some things that would be important for the general public to know about the issue?
- What do you think the general public will think about water reuse?
- What are some other solutions to our dwindling water resources?
The U.S. Congress passed two laws to protect our water. The Safe Drinking Water Act regulates what comes out of our taps. The Clean Water Act regulates what goes into our surface waters (including rivers, lakes, streams, and wetlands).
- What does the Safe Drinking Water Act require?
- What does the Clean Water Act require?
- What is the difference between the Safe Drinking Water Act and the Clean Water Act?
- Why do you think that Congress passed two different laws to protect our water?
Links between public health and water quality:
Water disinfection is considered by many to be one of the most important scientific advances of the 20th century. What kinds of health problems would we have if we didn’t disinfect our water? What kinds of health problems do people in places without water treatment suffer from?
What kind of information is found in a drinking water Consumer Confidence Report? What do we have the right to know about our water? What should immune-compromised people (such as cancer patients or the elderly) know about their drinking water?
How do water treatment facilities balance the risk between getting harmful bacteria and germs out of water versus putting harmful, cancer-causing chemicals in the water for disinfection?
Demonstrate how water filtration works using the EPA website for help.
Compare bottled water with local tap water. Have them both tested by the local water authority, do pH tests, Petri dish swabs, etc.
Visit your local wastewater treatment plant, drinking water filtration plant, local water source (such as a reservoir or lake).
Last updated: March 24, 2008
Amy Gambrill is an independent consultant who works in the United States and internationally on water pollution and wildlife conservation. She has been developing environmental science curricula and lesson plans for grades K-12 for more than 15 years. Ms. Gambrill has also taught environmental science to elementary school children.