Water Purification Process

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Importance of water

Water is key in supporting life on earth. Human beings require water on a daily basis for proper functioning of their bodies. Doctors usually recommend drinking eight glasses of water in 12 hours for a healthy living. Hence, water is an important element in the life of an individual. 

Scarcity or loss of water may cause dehydration and several health complications. It is the responsibility of the government to provide clean and safe drinking water to their citizens. Clean water makes sure that no pathogens/impurities are ingested by human beings. 

Purification of water is mandatory. It involves both physical and chemical processes. These processes help in making sure that water is safe and not actually harmful. 

Water purification is used for filtering impurities like bacteria and contaminants. It is important to apply physical and chemical methods of separation in an orderly manner while purifying water. 

For example, rain water is considered highly toxic. It contains several dissolved chemicals and dust. Even water from rivers is contaminated to a large extent.

Step-by-step process



The initial step in water purification is called aeration. Water is exposed to sufficient air in this process it is passed through special aeration tanks. Certain impurities which can interfere with the rest of the process are removed at this stage.

Carbon dioxide and iron oxide are removed from water. Chemical elements, water tastes and odor is removed in the ‘aeration’ stage.

Flash mixing

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The second step of water purification is called flash mixing. At times, this is the first step of water purification, as ‘aeration’ can be avoided depending on the status of raw water. It is during the second step that chemicals are added for eliminating impurities. Coagulation process takes place after flash mixing. 

In case the water is hard ( due to the presence of calcium and magnesium), lime and sodium carbonate are used for purification. If organic materials and bacteria are present, chlorine is added, it acts as a disinfectant. 

Agitation of water takes place for a period of thirty to sixty seconds. If flash mixing is done very fast, the rate of mixing of chemicals will be very poor. In case of excess mixing, floc is fragmented into finer particles. It is hence important to establish flow rate for regulating the time required for flash mixing. 

Coagulation is the third step in water purification. It is also known as flocculation. Complete reaction of mixed chemicals happens at this stage. It results in the formation of removable solid particles called flocs. If ‘mixing’ happens at a higher speed, flocs break down into smaller particles, which can be separated easily using several methods including filtration.

Hazy appearance of impure water due to the presence of soluble impurities is defined as its turbidity. Coagulation process is important for eliminating turbidity. It is difficult to disinfect water with high impurity. ‘Coagulation’ also helps in eliminating bacteria and color from water. Surface water has high turbidity when compared to groundwater.


Sedimentation process helps in removal of floc. In the process, water is passed through a sedimentation basin. The solid particles settle at the bottom of the basin according to their sizes, as a result of gravity. 

The large particles are definitely going to take their time in settling down. After this, water containing fine particles of floc moves to the  filtration stage. Most of the floc is removed in the filtration process, but still some tiny particles remain suspended in the water. Sand filtration is also applied on water.

It helps in purifying water. Sand filtration helps to remove more solid particles which get attached to the granules. Cleaning the sand occasionally ensures effective sand filtration. The practice helps in removing a covering of floc formed during filtration. The sheath is removed by pouring purified water on the sand, by hindering the flow of partially treated water.


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Once the water is purified, the disinfection process takes place, which is also called chlorination. It is very important for guaranteeing the safety of water before it is moved into the distribution system. Disinfection results in removal of bacteria. Basically, the disinfection process makes sure that water is free of disease-causing organisms when it gets distributed for drinking.

Chlorine is apt for disinfection owing to its properties. It is a strong oxidizing agent. It removes ammonia from water. Ammonia is not good for health. Chlorine is also responsible for the oxidation of iron, manganese, and hydrogen sulfide. In short, in addition to regulating the taste of water, it destroys organic matter as well.

An organized and well drawn-out procedure is required for obtaining safe drinking water. Water purification involves removal of impurities, micro organisms, organic matter, bad odor, color and other dissolved chemicals. The number of steps to be used for purification and the concentration of chemicals required largely relies on the nature of the raw water. 


Read more:Renewable Energy

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