Removing impurities from water


•      Water purification is the process of removing undesirable chemicals, biological contaminants, and suspended solids from contaminated water.

•      Water is purified for human consumption (drinking water) but water purification may also be designed for a variety of other purposes.


Removing Insoluble Impurities:

•      Insoluble impurities such as sand can be separated by:


•      Sedimentation is a physical water treatment process used to settle out suspended solids in water under the influence of gravity.

Figure 7: Sedimentation process

It involves the following Steps:

(1)   In this method, the mixture is allowed to stand undisturbed in a container.

(2)  After some time, the insoluble substances such as mud settle down at the bottom of the container as sediments. This process is called sedimentation.

•      Clean water can then be poured out into a separate container. This is called decantation.

Figure 8: Decantation process

•      The rate of sedimentation can be improved by adding special chemicals such as alum. This process is called loading.

•      Loading can be used to separate dirt particles suspended in muddy water.

Figure 9: Loading process is carried out to separate dirt particles



•      Filtration is the act and science of using filters.

•      In this method, insoluble impurities can be removed by passing the impure water through a filter paper.

Figure 10: Filtration process

•      There are many different methods of filtration, but all processes aim to attain the separation of two or more materials.

•      This is achieved by some form of interaction between the substance or objects to be removed and the filter.

•      In addition to this, the substance that is to pass through the filter must be a fluid, i.e. a liquid or gas.

Figure 11: Filtration process

•      A mixture of sand and water can be separated using filtration.


Removing Soluble Impurities:

•      It is more difficult to separate soluble impurities than insoluble ones.

•      Soluble impurities can be separated by:


•      Evaporation takes place, as molecules of water escape from a collective body of water like puddle, lake, or a stream.

•      Water molecules evaporate by taking up heat from the atmosphere.


•      The solution containing soluble impurities such as salt or sugar is heated.

•      After some time, the water changes into steam, leaving the impurities behind.

Figure 12: Evaporation process



•      Distillation is a widely used method for separating mixtures based on differences in their boiling points.

•      To separate a mixture of liquids, the liquid can be heated to change the components (which have different boiling points) into the gas phase. 

Figure 13: Distillation process

•      The water collected by this process is called distilled water.

•      Distilled water is the purest form of water and does not contain any impurities or germs.

•      It is widely used in car batteries, injections, and medicines.


Purifying Drinking Water:

•      Water may contain germs that can cause diseases.

•      Therefore, drinking water needs to be purified.

•      Drinking water can be purified using some methods like boiling, chlorination, filtration etc.



•      One of the simplest ways to purify drinking water is by boiling it.

•      Boiling water for about 10 minutes kills the germs present in water, making it safe for drinking.

•      Boiled water should be stored in clean and covered pots or pans.



•      Another method of purifying water is by adding a chemical called chlorine.

•      These days, chlorine tablets are easily available.

•      Adding chlorine tablets in water kills germs and makes the water pure.

•      This process of purifying water is called chlorination.