Water Quality

Both natural processes and human activities add pollutants and contaminants to water which is pure when first evaporated. The types of changes that may occur include:

1. Water vapor in the atmosphere condensing on small salt particles to form clouds and, ultimately, rain or snow
2. Particulate matter and gases mat be absorbed in clouds and be in precipitation as it falls to the earth
3. Surface water alters chemically as it contacts soil and other materials, through physical, biological, and chemical processes
4. Municipal, industrial, and agricultural activities add organic and inorganic pollutants to water
5. Groundwater is altered chemically and physically by the addition of minerals and gases dissolved from the rocks and soils through which it flows
6. Evaporation purifies water, changing it from liquid into vapor, but concentrates pollutants in the water which remains unevaporated.

Thus, water perpetually recycles and its quality continually changes.

The concept of water quality is meaningful only in the context of the use that is to be mode of the water. While most od us would consider distilled water to be pure and safe, the creatures that live in the sea would quickly die if placed in distilled water. Water high in plant nutrients, such as treated domestic sewage, may be an excellent source of water for irrigation, but it could cause serious problems when discharged to a surface water course. It has been said that "to live is to pollute." Even in the absence of human activity, other living organisms will pollute water. The question is not, "how do we completely abolish pollution?" but rater, "how can we improve water quality to a satisfactory level, and at what cost?"