Filtration:

As you have seen that sedimentation process reduces large percentage of suspended and organic load of raw water, the process of coagulation further helps in the removal of impurities present in colloidal form. But still, resultant water may not be up to desired standards and may contain impurities in the form of very fine suspended particle and micro-organisms etc.

To reduce or remove remaining impurities further, the water is passed through bed(s) of porous medium/media such as sand etc. The process of   removal of suspended or colloidal particle through passing the water through such medium/media is known as filtration.

The medium materials retain the impurities and allow the purified water to pass. The filtered water so obtained is relatively purer. Besides removing the turbidity filtration process is also helpful in the reduction or removal of other impurities such as color, micro-organism, and odour etc. from the water.