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Understanding Water Quality Issues and Pollution

Updated on July 15, 2012
More than 10% of our nations waterways are impaired.  This means that they are too polluted for humans or animals to use.
More than 10% of our nations waterways are impaired. This means that they are too polluted for humans or animals to use. | Source

It wasn't until the early 20th century that people began to care about what was in the water. Prior to this new awakening, it was believed that water could dilute any substance. As often would be the case, industrial effluent, raw sewage, and even animal waste would be dumped into the nearest river for disposal. Most people (and companies) at that time didn't really think about the damage that they were actually causing.

Today, we live in a much different world. There are a multitude of agencies that exist for the sole purpose of ensuring that our nation's water is clean. These agencies are charged with the duty to ensure that water pollution is minimized to the maximum practicable extent possible. In addition to this, the public is also more aware of the issues associated with water pollution then they were in the past. So what exactly constitutes water pollution anyway? Where does this pollution come from? And finally, how is it measured and detected?

Top 4 Pollutants in Our Water

  1. Hydrocarbons (petroleum)
  2. Raw Sewage
  3. Toxic Chemicals
  4. Heavy Metals

Water Pollution Defined

Essentially, water pollution is any substance that contaminates it and alters it's natural life-supporting ability. Additionally, water pollution is anything that can cause harm to humans, plants, and animals when consumed, touched, or inhaled. The list of substances that fit the description is nearly endless. Pollutants are divided into five general categories:

Disease Causing Agents - Things that can cause illness and disease fit into this category. This includes such things as Bacteria, Viruses, and various types of parasites.

Oxygen Demanding Substances - These substances are essentially the things that bacteria can consume. Bacteria require a lot of oxygen when they are breaking down organic matter. The main problems with these substances is that they remove dissolved oxygen from the water and encourage the growth of bacteria. When the oxygen is removed, the fish begin to literally suffocate.

Inorganic Substances - Many toxic chemicals and heavy metals are located in this category. These substances can cause birth defects, brain damage, and even cancer. Some of these substances are fat soluble as well. This makes them good candidates for bioaccumulation and biomagnification, further damaging the environment.

Nutrient Chemicals - If excess nitrates and phosphates are introduced into a body of water, it could cause eutrophication. An overabundance of these nutrients will allow algae to eventually become overgrown in a body of water. This overgrowth causes the oxygen supply in the water to disappear causing the fish to die. The algal blooms also block out the sun which prevents photosynthesis in other plants from occurring.

Sediments - Excessive sediments suspended in water can be considered a pollutant. The problem with sediments is twofold. First, sediments tend to block sunlight which can change the water's temperature as well as prevent photosynthesis from occurring. Second, sediments can carry pesticides and other chemicals into a body of water. Sediment is one of the main reasons water can have high turbidity.

Map showing the percentage of impaired waterways in the USA
Map showing the percentage of impaired waterways in the USA | Source

Where Does Water Pollution Come From?

Almost all pollutants found in our water are from anthropogenic sources. These include such things as transportation, mining, manufacturing, and even recreational activities. However, some pollution can come from mother nature. For instance, volcanic eruptions have been a major source of water pollution for millions of years.

Most pollution found in our water today also comes from nonpoint sources rather than specific companies and individuals. These means that the source of the contaminants are not directly attributable to any one single action or entity. An example of a nonpoint source of pollution is the exhaust generated the millions of cars on our roads. Pretty much everything that we do on a daily basis is contributing or has the potential to contribute to water pollution to some degree. Even the humble electric car still produces brake dust that can reduce the quality of stormwater runoff. Fortunately, the days where point sources dominated the water pollution market are long gone.

Fortunately, the days where point sources dominated the water pollution market are long gone. However, many point sources still exist. In today's society, farming facilities and wastewater treatment plants make up most of the point sources of water pollution.

Detecting and Measuring Water Pollution

There are a number of parameters and indicators that are used to assess the quality of a specific sample or body of water. These include such things as coliform bacteria, nutrient content, dissolved oxygen, pH, turbidity, and temperature.


Coliform Bacteria - If coliform bacteria is found in a sample of water, it usually means that it is contaminated with raw sewage. When testing a body of water, the amount of coliform bacteria, they are measured by running a standard total coliform test at 112F (44.5C). The results of these tests are reported as a Most Probable Number (MPN) index rather than a percentage or total count of bacteria. Just one coliform colony per 100ml of water is a major cause for concern.

Dissolved Oxygen (DO) - This parameter is used to assess the overall suitability of a water sample to support life. For example, fish typically require a minimum of 5mg of dissolved oxygen per liter of water to survive. However, it is recommended that DO levels be kept between 8-15mg/l to support all forms of life in the water. Measuring dissolved oxygen is accomplish by either using a standard DO probe and meter or the Azide-Winkler titration method. The former can be performed in the field and latter is typical done in the laboratory.

pH - The pH (or percent hydrogen) level of the water will indicate how acidic or alkaline it is. A healthy range for pH is between 6.5 and 8.0. If the pH gets too low toxic chemicals become easier to consume by aquatic plants and animals. Slight changes in pH can cause a significant loss of plant and animal life in a very short amount of time. Acid rain is one of the biggest contributors to pH changes in our nation's rivers, lakes, and streams. Testing the pH of water is very simple and can be done with some litmus paper. When dipped in water, the paper changes color to correspond to a specific level of acidity or alkalinity.

Turbidity - This is an indicator of the clarity or transparency of the water. High levels of turbidly can block sunlight and allow the water's temperature to change. Visible contaminants in the water can also hinder a fishes ability to breath. In addition to this, when the floating particles settle out they can smother plants growing at the bottom of a lake. Testing for turbidity is sometimes accomplished by performing a visual assessment in the field. However, more often then not turbidity is measured by placing a sample of the water in a turbidimeter which measures the percentage of light that shines through it.

Temperature - Temperature is a measure of the amount of heat energy that is in the water. Temperature is important because it is a key variable in many of the natural chemical and biological processes that occur in water. There is also a direct and proportional relationship between water temperature and the rate that photosynthesis in plants can occur. Temperature affects and the amount of oxygen that can be dissolved in the water as well as an animal's sensitivity to toxic chemicals. The temperature is measured using a simple thermometer.

Nutrient Content - Nutrients found in water will typically be composed of nitrates and phosphates. Although these compounds are required for plants and animals to grow, too much of them can cause eutrophication. Under normal conditions, nitrate concentrations are usually less than 1 mg/L. For comparison, treated wastewater sometimes has a nitrate concentration of more than 30 mg/L. Phosphorus is a major chemical of concern. It only takes a minuscule amount of phosphorus to cause a water body to begin to eutrophy. Sources of phosphorus include wastewater treatment, stormwater runoff from farm fields, and cleaning chemicals. There are a number of laboratory based methods to test for the concentrations of these compounds. The preferred method is the use of nutrient test strips because they are easy to use and can be used in the field.


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