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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 runoff or 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
http://www.epa.gov/safewater/kids/grades_4-8_water_filtration.html
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 www.epa.gov/surf
or http://water.usgs.gov/wsc/
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 diagrams online at http://www.wcrsaonline.org/images/treatment-process-10-2-06.jpg
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?
Water legislation:
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? Labs:
Demonstrate how water filtration works. Visit http://www.epa.gov/safewater/kids/grades_4-8_water_filtration.html Compare
bottled water with local tap water. Have them both tested by the local water
authority, do pH tests, Petri dish swabs, etc. Field Trips:
Visit your local wastewater treatment plant, drinking water filtration plant,
local water source (such as a reservoir or lake). |
