Steps In Water Treatment


In its natural state, water and ions present in it are pure. However, during flow and distribution, it comes in contact with impurities such as magnesium ion, lead, bacteria, and viruses, leading to contamination. This contamination makes it unfit for drinking. Thus the need for water to be treated.

Although there are a variety of options available for treating water, particularly in large-scale production. The basic steps involved as well as the end goal are the same.

Listed below are steps involved in water treatment.


Coagulation is the addition of a coagulant, usually aluminum sulfate (commonly referred to as alum) to raw water. The effect of the alum makes impurities in the resulting mixture coagulate. This mass of dirt is referred to as flocs. These flocs can then be separated from water through filtration or sedimentation. Other coagulants like ferric sulfate and sodium aluminate can also be used.

Coagulation is achieved in two stages; slow mixing and rapid mixing.

● Rapid mixing

Rapid mixing helps distribute the coagulant properly. This ensures a better chemical reaction. Rapid mixing is achieved by adding coagulants before the pump.

● slow mixing

On the other hand, slow mixing is achieved by prolonging the detention time. It involves the slow movement of the mixer.


This is the next step after flocculation. Here, the water and flocs are slowly moved into the sedimentation tank. This slow movement allows the heavy floc particles to sediment. Sedimented flocs found at the bottom are referred to as sludge. This sludge from here is moved to a lagoon while pure water flows to the next phase which is the filtration tank.

In a treatment process that involves direct filtration, the filter removes the floc thus omitting the sedimentation phase.


Filtration involves the use of a filter to remove unwanted particles from the water. Filters are made from different materials and come in various forms.

Here are some forms of filters available.

  • Activated Carbon: It is good for removing chemicals, organic, and inorganic substances. Activated carbon is produced when a material with high quality of carbon is charred. Examples include wood, coal, or coconut shell. It filters by a process called adsorption. In adsorption, impurities in the water bind to the charred substance, thus pulling them out of water.
  • Ion Exchange: Just as the name implies, it works by exchanging one ion for another. For instance, in relatively hard water, the calcium or magnesium ions responsible for water hardness are exchanged for sodium ions. This method is good for treating hard water and removing radioactive material.
  • Reverse osmosis: This makes use of a permeable membrane. It works by using pressure to push contaminants like fluoride, arsenic, nitrate, copper, etc to one side of the membrane and the filtered water to the other side of the membrane. It is an effective method for removing water-soluble contaminants as well as bacteria.
  • Mechanical Filter: It is used for the removal of physical particles. Particles are filtered with help of nylon flush, in pad material, or synthetic foams. This method is used in fish ponds to remove waste material and leftovers.
  • Ultra Violet Filter: Ultra Violet light of various frequencies is used for the removal of bacterial and viruses. This method is used in combination with other filters as it does not remove other forms of impurities like lead, chlorine, and pesticides.


At this stage, pathogenic microorganisms like bacteria, parasites, and viruses are removed with disinfectants before it is being passed to the next stage. Chlorine is the most commonly employed disinfectant.


Fluoridation is a process used to increase the concentration of fluoride ions in water. Fluoridated water prevents tooth cavities and decay. Community fluoridation of water has been recommended by public health organizations. It is also one of the most cost-effective and efficient means of ensuring that everyone has access to adequate fluorine regardless of social status.


This is the process of neutralizing the PH of the water. In its natural state, water is meant to have a PH of 7. Once it is above or below this, it needs to be corrected. PH correction also helps to reduce corrosion in water systems.


This involves the removal of solid waste that has been accumulated from the process of sedimentation.

The steps involved in water treatment may be slightly different depending on the system and technique employed, but the above-listed methods are the basic and generally accepted steps in water treatment.

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