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12.27: Sources of Water Pollution

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Is the ocean a good dumping ground?

Unfortunately some people think so. A lot of garbage ends up washing ashore, and some garbage stays floating out in the ocean. Animals can be strangled by floating trash or mistake inedible trash for food. Not only is the pollution of our oceans a problem, but also our precious freshwater resources are often polluted.

Sources of Water Pollution

While to many people clean water may seem limitless and everywhere, to many others this is not so. Water pollution is a serious issue facing hundreds of millions of people world-wide, having harmful effects on the lives of those people. Water is not in unlimited supply and cannot just be made fresh when it is wanted. Water is actually a limited resource, and for many people, fresh, unpolluted water is hard to find. A limited resource is one that we use faster than we can remake it. It is a resource that can be used up.

Water pollution happens when contaminants enter water bodies. Contaminants are any substances that harm the health of the environment or humans. Most contaminants enter the water because of humans.

Water pollution can cause harmful effects to ecology and human health. Shown is the pollution in Jakarta, Indonesia.

Natural events, like storms, volcanic eruptions and earthquakes can cause major changes in water quality. But human-caused contaminants have a much greater impact on the quality of the water supply. Water is considered polluted either when it does not support a human use, like clean drinking water, or a use for other animals and plants. The overgrowth of algae, known as an algal bloom , can result from the runoff of fertilizer into bodies of water. This excess of nutrients allows the algae to grow beyond control, bring harm to the rest of the ecosystem.

The main sources of water pollution can be grouped into two categories:

  • Point source pollution results from the contaminants that enter a waterway or water body through a single site. Examples of this include untreated sewage, wastewater from a sewage treatment plant, and leaking underground tanks.
  • Nonpoint source pollution is contamination that does not come from a single point source. Instead, it happens when there is a buildup of small amounts of contaminants that collect from a large area. Examples of this include fertilizer runoff from many farms flowing into groundwater or streams.


  • algal bloom : Over-growth of algae that can lead to oxygen depletion and fish kills.
  • contaminant : Substance that harms the health of the environment or humans.
  • limited resource : Resource that is used faster than it can be made.
  • nonpoint source pollution : Contaminants that build up from small amounts of contaminants that collect from a large area.
  • point source pollution : Contaminants that enter a water body through a single site of entry.
  • water pollution : Pollution due to contaminants entering the water supply.


  • Water is a limited resource, but it is often polluted by humans.
  • Sources of water pollution can be grouped as point source pollution (large amounts entering through a single site) or nonpoint source pollution (small amounts entering from many sites.)


Use the resource below to answer the questions that follow.

  1. How can human sewage throw ecosystems out of balance? What nutrient cycle(s) are involved?
  2. How is the nitrogen cycle impacted by agriculture run-off? How does this change move through the food web? What can the result be?
  3. How can drugs excreted by humans affect aquatic organisms? How does this affect the ecosystem?
  4. What is heat pollution? What affect can this have on aquatic ecosystems? Explain your answer as fully as possible.


  1. What are some sources of water pollution?
  2. What's the difference between a point source and nonpoint source of water pollution?

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Difficulty Level:

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7 , 8

Date Created:

Nov 29, 2012

Last Modified:

Nov 04, 2014
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