Stages of Water Purification

Updated February 21, 2017

In most cases the water you drink from the faucet is not pumped straight from nature ready for consumption. Drinking and bathing water must undergo a purification process to ensure safety for consumers. This extensive process is broken down into several stages so that the water leaving a purification plant is as clean as it can be before people come in contact with it.


The preliminary purification stage is the first line of defence against contamination. Here the water enters the facility through a series of screen filters that remove large particles such as rocks, sticks, leaves and other debris or waste to prepare the water for the primary purification, which involves several more stages. The first chemicals are also added during primary purification to prevent the growth of algae as the water undergoes further stages, according to the All Water Purification website. Aeration or churning is also part of the process, which removes gasses from the water to prevent foul taste or smell.


The coagulation stage of water purification involves the addition of alum to the water. Suspended material within the water such as silt and microbes are too small for filters to remove effectively, so the alum helps to coagulate, or clump them together, so that the filters and screen will strain off the impurities during the next stage.


Flocculation is the removal of the particles coagulated in the previous step. This stage of purification is quite slow because the water has to move very slowly or remain still so that the heavier coagulated lumps of impurities will sink to the bottom and settle or float as a film on top of the water.

Clarification is the second part of this stage, in which the sludge settled to the bottom of the tank or floated to the top is removed.


The calcium and other minerals present in water are not likely to be completely removed during the previous purification process stages, resulting in a very hard water product in some areas. Hard water can cause problems with pipe corrosion, decrease the ability for detergents to do their jobs and leave annoying white build-up on showers, sinks and dishes. To rid the water of these abundant minerals and any other remaining impurities, the water is passed through sand filters to trap the remaining particles, according to the Battle Creek Area Clean Water Partners website.


In the final stage of water purification, the treatment plant puts additives into the water. These additives may include lime or phosphates to help reduce water hardness and protect pipes. Chlorine is typically added to disinfect water and to prevent future growth of pathogens. Fluoride is also added in some areas to prevent tooth decay, according to the Battle Creek Area Clean Water Partners website.

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About the Author

Lee Morgan is a fiction writer and journalist. His writing has appeared for more than 15 years in many news publications including the "Tennesseean," the "Tampa Tribune," "West Hawaii Today," the "Honolulu Star Bulletin" and the "Dickson Herald," where he was sports editor. He holds a Bachelor of Science in mass communications from Middle Tennessee State University.