Chapter 5—The Water We Drink
30 March 2008
5.2—Where Does Drinking Water Come From?
-Water is found underground in aquifers, great pools of water trapped in sand and gravel 50-500 feet below the surface.
-Water than can be made suitable for drinking comes from either surface water or groundwater. Surface water, water from lakes, rivers, and reservoirs,
frequently contains substances that must be removed before it can be used as drinking water. Groundwater, water pumped from wells that have been
drilled into underground aquifers, is usually free of harmful contaminants. Large-scale water supply systems for cities tend to rely on surface water
resources. Smaller cities, towns, and private wells tend to rely on groundwater, the source of drinking water for a little over half the U.S. population.
-The great majority of Earth’s water, 97.4% of the total, is in the salty oceans, water that is undrinkable without expensive purification. The remaining
2.6% of Earth’s total water is all the fresh water we have. The majority of even this relatively small supply of fresh water is permanently frozen in
glaciers and polar ice caps. Only about 0.01% of Earth’s total water is conveniently located in lakes, rivers, and streams as fresh water.
5.3—Water as a Solvent
-A major reason we must consume water is that it is an excellent solvent for many of the chemicals that makes up our bodies, as well as
for a wide variety of other substances. A solvent is a substance that is capable of dissolving other substances. Solutions are those
substances that dissolve in the solvent. The resulting mixture is called a solution, a homogenous mixture of uniform composition.
Furthermore, aqueous solutions are solutions in which water is the solvent.
-Because water is such a good solvent, drinking water is rarely, if ever, just “pure” water. Municipal water companies provide
information about the dissolved mineral content, the solutes, for tap water.
Importance of Water as a Solvent
In Our Bodies
In the Environment
-Blood plasma is an aqueous solution containing a variety of life-
-Inhaled oxygen dissolves in blood plasma in the lungs, allowing
to combine with hemoglobin.
-Blood plasma carried dissolved carbon dioxide to the lungs to be
-Water helps to maintain a chemical balance by carrying wastes