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6.17: Protecting Water From Pollution

Difficulty Level: Basic Created by: CK-12
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How could a river burn?

In the mid 1900s, rivers sometimes caught fire. The Cuyahoga River did several times. The river was so full of oil and industrial waste that it was flammable. Nothing could live in it. A fire on the Cuyahoga River in 1969 gained national attention. Something had to be done to protect the water supply.

Protecting the Water Supply

The water supply can be harmed in two major ways. The water can be polluted, and it can be overused. Protecting the water supply must address both problems. We need to reduce how much pollution ends up in the water supply—keeping water from being polluted is easier and cheaper than cleaning it. We need to treat water that’s already polluted. We need to conserve water by using less.

Controlling Water Pollution

Disasters, such as rivers burning, led to new U.S. laws to protect the water. For example, the Environmental Protection Agency (EPA) was established, and the Clean Water Act was passed. Now, water is routinely tested. Pollution is tracked to its source, and polluters are forced to fix the problem and clean up the pollution. They are also fined. These consequences have led industries, agriculture, and communities to pollute the water much less than before.

The Clean Water Act

Keeping water clean often requires laws. Laws ensure that people behave responsibly. The Clean Water Act regulates water pollution in the U.S. The law allows the EPA to set standards for water quality. The EPA regulates the pollutants that can enter waterways. The agency can provide money for wastewater treatment plants. The law was passed in 1972.

International groups are trying to improve global water quality. The United Nations and other groups provide the technology for treating water. They educate people in how to protect and improve their water (Figure below).

Scientists studying water pollution

Scientists control water pollution by sampling the water and studying the pollutants that are in the water.

Water Treatment

Water treatment is a series of processes that remove unwanted substances from water. The goal of water treatment is to make the water safe to return to the natural environment or to the human water supply. Treating water for other purposes may not include all the same steps. That’s because water used in agriculture or industry may not have to be as clean as drinking water.

Below, you can see how water for drinking is treated (Figure below). Treating drinking water requires at least four processes:

  1. Chemicals are added to untreated water. They cause solids in the water to clump together. This is called coagulation.
  2. The water is moved to tanks. The clumped solids sink to the bottom of the water. This is called sedimentation.
  3. The water is passed through filters that remove smaller particles from the water. This is called filtration.
  4. Chlorine is added to the water to kill bacteria and other microbes. This is called disinfection. Finally, the water is pure enough to drink.

Coagulation, sedimentation, filtration, and disinfection are the four steps of treating water

Four processes are used to treat water to make it safe for drinking.

What Can You Do?

What can individuals do to protect water quality?

  • Dispose of motor oil and household chemicals properly. Phone your community for instructions.
  • Use lawn, garden, and farm chemicals sparingly. Use them wisely. Excess chemicals will run off into the water supply.
  • Repair automobile or boat engine leaks immediately.
  • Keep litter, pet waste, leaves, and grass clippings out of street gutters and storm drains.

Science Friday: Poop and Paddle: An Eco-Friendly Floating Toilet

How do wetlands filter water? In this video by Science Friday, inventor Adam Katzman describes how his toilet-boat converts human waste into cattails and clean water.


  • There are multiple levels of water treatment. Some water is cleaned enough for use on lawns. Some must be made safe for drinking.
  • Individuals can protect water by following some guidelines.
  • The Clean Water Act regulates pollutants and provides money for wastewater treatment plants to be built.
  • Keeping water from becoming polluted is easier, less expensive, and safer than cleaning it once it is polluted.


  1. How is water treatment better than water cleanup later?
  2. How is wastewater treated?
  3. What can you do to protect water quality?
  4. What is the purpose of the Clean Water Act?

Explore More

Use this resource to answer the questions that follow.

  1. What crises led to the Clean Water Act?
  2. What did people demand on Earth Day in 1970?
  3. Which president created the EPA?
  4. What did the Clean Water Act do?
  5. What happened to the Clean Water Act after it passed through Congress? What did Congress do then?
  6. What did the EPA ban?
  7. Why was the Potomac River so smelly?

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coagulation In water treatment, chemicals cause solids to clump together.
disinfection In water treatment, chemicals kill microbes.
filtration Water passed through filters that remove small particles.
sedimentation In water treatment, clumped solids sink to the bottom of the tank.

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Difficulty Level:
6 , 7
Date Created:
Jan 04, 2013
Last Modified:
Dec 23, 2016
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