1.1: Water Resources and the Origin of Contaminants
After reading this section, you should be able to:
- Understand and describe water sources
- Describe the water cycle
- Compare the term water contaminants with water pollutants
This chapter presents a brief introduction to the water sources that are available for potable supply; detailed information is presented in Water 132 (Water Supply). Understanding drinking water sources is important to assess the variety of contaminants that can be present in water.
Water Sources
According to the United States Geological Survey (USGS), 71% of the Earth’s surface is covered in water, and of that 97% are the oceans. The Earth’s water can be broken into two different categories: freshwater and salt water. Fresh water is simply water that is not salty and can be found in the planet’s surface water such as streams, lakes, and frozen as ice, but also underground in aquifers. Fresh water is stored on the surface as surface water or stored underground in aquifers as groundwater . Salt water can be found in the world’s oceans.
Figure 1.1.1 shows that our planet’s water sources are limited. Freshwater is much easier to use for potable (drinkable) applications because it requires simpler treatment. However, it represents only a small fraction of the Earth’s water portfolio. A large proportion of the freshwater is locked in glaciers and is not accessible. As a result, less than 1% of the water present on the planet is groundwater and surface water that can be more easily used as potable water source. Although desalination plants have become more prevalent, they are very costly, and their overall environmental impacts are unknown.
Figure 1.1.1: Distribution of Earth’s Water.
The origin of a water source determines its characteristics and the presence of specific contaminants. The concentration and composition of contaminants in water is also influenced by the movements of water, which is illustrated by the water hydrologic cycle (Figure 1.1.2). The Water Cycle is both driven by gravity (i.e., water flows downhill) and sunlight (i.e., water evaporates and condenses).
Figure 1.1.2: Water Hydrologic Cycle
Classifications of Contaminants
According to the Safe Drinking Water Act, a contaminant is any physical, chemical, biological, or radiological substance in water. While some contaminants are harmless, others are deadly. Contaminants can even mix with water molecules in the atmosphere. Technically, any compound that is not a water molecule is a contaminant when it comes to water.
Many people think that all contaminants are manmade. They are not! Some have natural sources in the soil, such as arsenic and uranium. These can be expensive to remove because they occur naturally in the rocks around the water source.
Water can be contaminated by various human-caused ( anthropogenic ) activities or by existing natural features ( natural contaminants ) like mineral-rich geologic formations. It is not uncommon to find naturally occurring fluoride or arsenic in water.
Agricultural activities, industrial operations, landfills, animal operations, and small and large scale sewage treatment processes, among many other things, all can potentially contribute to contamination. As water runs over the land or infiltrates into the soil and groundwater , it dissolves material left behind by these potential contaminant sources.
There are three major groups of contamination: inorganic chemicals, organic chemicals, and biological agents. The risks and type of remediation for a contaminant depend on the type of chemicals present.
People use the words contaminants and pollutants interchangeably. What is the difference between a contaminant and a pollutant?
- A contaminant is a substance that is not normally expected.
- A pollutant is a substance found at a concentration that has reached a level that adversely affects the suitability of the water for its intended purpose.
Key Terms
- anthropogenic contaminants – human-caused (manmade) contaminants
- contaminant – a substance that is not normally expected
- groundwater – water stored in the ground
- natural contaminants – contaminants in soil geology, erosion of soils, etc. Examples of contaminants include fluoride and arsenic
- pollutant – a substance found at a concentration that has reached a level that adversely affects the suitability of the water for its intended purpose
- surface water – water on the surface of the earth
Review Questions
- Outline the water cycle highlighting water sources.
- List the major contaminants of water in the environment.
Chapter Quiz
-
How much water on planet earth is easily treated for drinking water?
- 96%
- 20.9%
- 32%
- < 1.0%
-
Most of the water on earth is found in the _________.
- atmosphere
- ocean
- ground
- rivers
-
Which of the following is a natural contaminant?
- Pesticides
- Nitrates
- Phosphates
- Fluoride
-
Anthropogenic contaminants refers to __________.
- turbidity
- geological contaminants
- inorganic contaminants
- manmade contamination
-
The ________ is(are) essential for the maintenance of most life and ecosystems on the planet.
- climate
- water cycle
- aesthetic characteristic of water
- atmospheric circulation
-
The ______ drive(s) the water cycle.
- types of precipitation
- oxygen concentration
- nutrient levels
- sun
-
What portion of surface water is found in the permafrost and ice?
- 69%
- 68.7%
- 96.5%
- 30.1%