Water Pollution

Water Pollution is any Chemical, Biological, or Physical change in water quality that has a harmful effect on living organisms or makes the water unsuitable for desired uses. There are two main types of pollution sources:

Non-point versus Point Source Pollution

Examples of Water Pollutants

  • Sediment
  • Infectious Agents
  • Oxygen-Demanding Wastes
  • Organic Waste
  • Inorganic Chemicals
  • Plant Nutrients
  • Radioactive materials
  • Heat or Thermal Pollution

Point Source Pollution

If you can point to the pipe that the pollution is coming out of, then you are looking at Point Source Pollution.

Examples: Effluent pipes (pipes leaving the site) from Sewage Treatment Plants, Smokestacks from Factories, Automobile Tailpipes, Abandoned Underground , Oil Tankers

Non-Point Source Pollution

Even if you know who or where the pollution is coming from, it is Non-Point Pollution if there is no specific site where the pollution enters the Air, Water, or Land. If you can't point to a pipe, it's Non-Point Source. The most common word associated with Non-Point Pollution is Runoff.

Examples: Acid Deposition, Runoff from Croplands, Livestock Feedlots, Logged Forests, Urban Streets, Lawns, Golf Courses, Parking Lots.

Point and Non-Point Sources of Pollution

Other Key Definitions for Water Pollution:

  • Dissolved Oxygen (DO): The amount of oxygen that is present in the water, usually measured in mg/L or parts per million (ppm.) Aquatic organisms need DO to live and there must be a minimum of 5 parts per million in order to sustain life. <2 ppm = dead, 2 to 4 ppm = stressed, >5 ppm = sustainable
  • Biological Oxygen Demand (BOD): The amount of Dissolved Oxygen demanded by aerobic organisms to break down organic material in a sample of water. When sewage or other oxygen demanding wastes enter the water, dissolved oxygen decreases, and the demand for oxygen increases be used to break down the sewage. So if DO decreases, then BOD increases. SEE OXYGEN SAG CURVE BELOW.
  • Inorganic Nutrients: Nitrates and Phosphates are not carbon based and are therefore inorganic. However, they are used in fertilizers to provide plants with what they need to grow. Nutrients are great for plants, but bad for water due to the growth of algae. Nitrates come from fertilizers and animal waste, and Phosphates come from fertilizers, decomposition, and from household cleaners.
  • Turbidity: the clarity or the cloudiness of the water. Usually measured by shining light through a water sample to see how much light is refracted. The more light that gets refracted, the higher the number (in Nephelometric Turbidity Units or NTU's) and more turbid the water is.
  • Thermal Pollution: The hotter the water gets, the more the water molecules expand and force out any oxygen that was between the water molecules. Colder water has more Dissolved Oxygen than warmer water. Factories in the U.S. are required to cool the water they use in the industrial process before they can return the water to the ecosystem.

Oxygen Sag Curve

The curve obtained when the concentration of dissolved oxygen in a river into which sewage or some other oxygen demanding waste has been discharged is plotted against the distance downstream from the sewage outlet

What are the names of the zones, and what types of organisms would you find in them if an oxygen demanding waste entered a body of water?

What is the worst thing that we can allow into our waterways?


Sediment is the carrier of all of the other answers you may have thought of in the question above. Why is dirt the worst thing we allow to get into water?

  • It fills the pore spaces between sediment where fish might lay their eggs.
  • Sediment makes the water turbid, or cloudy, which absorbs the sun's light and raises the temperature of the water.
  • Filling a body of water with sediment means less volume for aquatic organisms to grow in.
  • Inorganic nutrients, oxygen demanding wastes, fecal coliform, and other pollutants runoff with the sediment into bodies of water.

When Inorganic plant nutrients runoff in sediment into the nearest body of water, the following is what happens:


This is arguably the biggest buzzword in APES! Make sure you understand the entire process, because this is guaranteed to be on our test and on the AP Exam. Cultural Eutrophication means that the source of the nutrients and erosion was human activity.

  1. Sediment runoff carries inorganic plant nutrients (Nitrates and Phosphates) from fertlizers, animal waste, and decomposition into a body of water.
  2. The Nitrates and Phosphates cause Algal Blooms to appear. (When algae grows and dies quickly.)
  3. The sediment and algae fills the body of water which absorbs heat, raising the temperature of the water and forcing dissolved oxygen out.
  4. The algae blocks the sunlight from reaching the other aquatic plants, so decomposing bacteria begin to consume the dead algae and plants. The bacteria need Dissolved Oxygen to decompose, so more oxygen is lost.

So Eutrophication is ultimately the death of a body of water due to the loss of Dissolved Oxygen. The three things that cause the body of water to lose oxygen are the raising of the temperature of the water (thermal pollution), the decomposition by bacteria of the algae in the algal blooms, and the decomposition by bacteria of the native aquatic plants and animals that cannot get sunlight or oxygen anymore.

The EPA estimates that 85% of all large U.S. lakes suffer from this.

What are some solutions for eutrophication?

Riparian buffers

Riparian Buffers are zones of vegetation that help to stop sediment from running off into water, and by holding the sediment down with root systems.

The plants benefit from the plant nutrients that are in the sediment and use them to grow rather than allowing the Nitrates and Phosphates to get into the water and form algal blooms.

Some plants can even absorb heavy metals like mercury when used around mining areas.


Providing a constant source of Dissolved Oxygen for bodies of water that are stagnant will help prevent algal blooms from forming. Fountains are a great way to help save a pond or a lake from eutrophication.

Oxygen is a powerful sterilizing agent and is used in sewage treatment plants to reduce the amount of harmful bacteria in waste by spraying water into the air. Spraying wastewater allows for other dissolved gases like CO2 to be removed, and for dissolved metals like iron, hydrogen sulfide, and VOCs to be oxidized for easier removal.

Groundwater Pollution

Groundwater is a major source of drinking water and irrigation, especially for coastal areas.

There are approximately 750,000 Underground Storage Tanks in the U.S. About 1/3 of those are leaking into our groundwater. Non-degradable wastes are never recovered, and since there are fewer bacteria underground, even degradable waste can take hundreds to thousands of years to recover.

Contaminated aquifers are nearly impossible to clean up, so PREVENTION is the key to groundwater pollution.

We prevent groundwater pollution by:

  • Monitoring aquifers near landfills
  • Use leak detection technology on the underground storage tanks
  • Ban/regulate disposal of hazardous wastes in landfills
  • Store hazardous waste above ground.
Created By
Mark Townley

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