Describe the mechanical and chemical processes required to prepare water for human consumption ...

The mechanical and chemical processes used to prepare water for human consumption consist of three stages. In
the first stage, larger pieces of solid materials that are floating or suspended in the water are filtered out. In the
second stage, smaller particles are coagulated into larger clumps that can be allowed to settle out in the form of
sedimentation. During both the first and second stages, biological decomposition of organic contaminants takes
place and most of the resulting decomposed materials are either filtered or settled out. During the third stage,
chemical treatment of the water is used to remove most of the remaining impurities.

Three kinds of contaminants are normally found in almost all naturally occurring water: chemical impurities,
biological impurities, and turbidity

Each year about 119,000 cubic miles of water enters the water cycle through evaporation and falls to the earth in
the form of precipitation. Of that amount, humans use about 700 cubic miles of water annually. The movement
of water through most of this process occurs without human intervention. That is the natural water cycle. When
humans divert part of the water for their own use, the diverted water enters the human water cycle. Even though we
say that humans use 700 cubic miles of water annually, practically none of the water is used up because most of it is
returned to the natural water cycle immediately and almost all of the rest eventually moves back into the water cycle.

Primary treatmentcollects waste water and removes items that settle out of it.
 Secondary treatmentinvolves biological processing of sewage.
 Tertiary treatmentinvolves the chemical processing of sewage