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Water Cycle
Beginning the Cycle
Twenty thousand feet above the surface of the earth, water molecules change from vapor to liquid in a storm cloud building over a range of mountains. The water falls to earth as rain and flows down through mountain streams to a large reservoir which serves as the source of drinking water for a city. Ultimately, it flows through the water supply system and into a home where a teenage boy uses it to brush his teeth on a Saturday morning.

At this point the water begins its return trip to nature. It drains from the bathroom sink into the community's sanitary sewer system which leads to the public treatment plant. Here it is joined by millions of litres of wastewater coming from other homes, businesses, industries, and institutions, and is treated by a variety of processes to remove pollutants.

After Treatment
After treatment, the cleansed wastewater is released to a lake, stream, or river, where it flows toward one of the great oceans. It will be used again by other people along the way for irrigation, by industry, as drinking water, or it will evaporate into the atmosphere and return again as rain in some other part of the world. This example illustrates two important points:

Water is a finite resource; we have all that we will ever get. It is used over and over again, and its cleanness must be protected.

Your public wastewater treatment plant stands at a critical point in this water cycle. It helps nature's way of cleaning water and is a last defense against the polluting of our water supplies. 

Copyright © 1985 by WEF