The 5 major unit processes include chemical coagulation, flocculation, sedimentation, filtration, and disinfection (described below). There are chemicals added to the water as it enters the various treatment processes.

Gather water from your natural environment. 
Create a basic purification filter if the only available water source is contaminated with dirt particles or other debris.
Boil the filtered water.
Apply chlorine bleach whenever boiling water is impractical or impossible.

Step One:
Screening. Source water, either from a natural source or from an industrial one, will typically pass through a screen as it enters industrial filtration systems.
Step Two:
Step Three:
Step Four:

Water that is safe for drinking is called potable water. The treatment piece of this process is called the water-treatment process.Disinfection is the use of chemical and/or other means like UV radiation to kill potentially harmful microorganisms and pathogens in the water.

Drinking water, like every other substance, contains small amounts of bacteria. Chlorine is usually added to drinking water to prevent bacterial growth while the water streams through pipelines.

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