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How Do Water Filters Work?

an animated portrayal of a man standing beside water filter system

Water filters are used to purify our drinking water from the impurities and contaminants effectively. The purification efficiency differs from filter to filter. There are different kinds of water filters for water purification. Each type of filter is particularly effective in removing certain impurities. A single filter can never eliminate all the pollutants and contaminants that are present in the water. Therefore, in most of the purification systems a combination of two or more than two filter systems are installed for effective purification.

The main purpose of these water filters is to remove unwanted and disease causing impurities from the water that we consume in our daily lives. These filters cannot kill the germs present in the contaminated water rather they prevent these impurities from passing on to our drinking water, hence saving us from the severe health consequences. Some of the contaminants can cause serious health issues that pollute our drinking water.

Stages in Water Purification System:

The mechanism of these water filters is almost the same in every purification system. The filtration process of drinking water is mainly composed of five stages that are as given as follows:

  1. Sediment
  2. Mechanical
  3. Chemical
  4. Mineral
  5. Bacterial

The different purification processes used in these filters can be Reverse Osmosis Water Filtration, Ultra Filtration, and Ultra Violet Disinfection. In this regard the quality and nature of water is also important. The kind of filter that is suitable for your water purification is determined by the quality of water. The different sources of water have separate features that are added with the water along with their particular impurities and contaminants. The kind of filter should be selected according to the quality of water.

Basics of Water Filters:

The function of water filters is to block the contaminants and impurities in the form of germs, bacteria, viruses and other metallic substances from passing on to our drinking water. There is a porous membrane through which water is passed where the small openings allow pure water and retain the impurities. The efficiency of these filters depends on the size of these pores that determine the quality of purified water. These pores are of microscopic nature hence themeasurements of the pores’ size are also microscopic.

The measurement of these pores’ size is called micron. The size of one micron is 1/1000 of a milliliter. One micron-sized filters can easily parasites, their eggs and larvae, and protozoa from the water. However, in order to filter out bacteria from the water, you need to have a filter with size of 0.4 micron.

An Image displaying a pool water filtration system

Techniques Used in Water Filters:

There are two types of techniques used in water filters to remove the impurities which are as given as follows:

  • Physical Filtration:

Physical filtration involves a physical filter through which water is rinsed to remove the harmful contaminants and other impurities. The physical filter acts as a sieve or thin piece of textile that works as a filtering membrane to separate the pollutants and impurities from the water.

  • Chemical Filtration:

Chemical filtration involves the purification of water through chemical process. It involves a chemically active substance that actively removes impurities from the water.

Types and Working Mechanism of Water Filters:

In order to understand the functioning mechanism of water filters, we are going to discuss some of the main types of these filters along with their way of working. Each of these filters types are designed to overcome certain problems. Most of the time, the filtration system is composed of two or than two filter combinations for better functioning and enhanced results. Some of the important types of filters are as given as follows:

1. Mechanical Filters/ Sediment Filters:

Mechanical filters involve the removal of impurities and contaminants physically through a barrier in the form of filter or porous membrane. The efficiency of mechanical filters is determined by the size of their respective microns hence eliminating the risk of impurities accordingly.

  • With the size of 5-micron, these filters can remove visible impurities from the water. So, basically they are best for the purification of all the contaminants that can be spotted by our naked eyes.
  • 1 micron sized mechanical filters can effectively remove microscopic level impurities.
  • 5 micron sized mechanical filters can further eliminate the risk of pathogens i.e. giardia and cryptosporidium.

2. Absorption filters:

In absorption filters, activated carbon granules are used for the purification of water. These carbon granules are highly active in capturing the impurities and contaminants that are present in the unprocessed water. The reason of this trapping capability of these activated carbon granules can be attributed to the fact that they have considerable internal surface that is perfectly packed with corners and cracks. These enormous surfaces can easily trap chemical contaminants too i.e. chlorine.

Domestically, most common used filters have activated carbon granules. In addition to that,due to their absorbing capability, they are highly effective in eliminating unpleasant odor and unwanted tastes from the purified water.

For absorption filters, carbon can be manufactured from different sources like burning wood and coconut shell etc. The filters made up of coconut shells are more effective as compared to the other source i.e. wood, however, they are expensive too.

3. Sequestration Filters:

Sequestration filters are used to isolate the substances chemically in the water. The main function of these filters is to soften the water by removing lime scale and reducing the risk of corrosion. For the purpose, food grade polyphosphate is used in scale constraining filters in order to isolate minerals like calcium and magnesium which can result in to lime scale and corrosion.

Technically, polyphosphate used in these filters does not soften the water, rather, it functions to retain these minerals within the water. Hence, it prevents these minerals to form a lime scale upon encountering any surface.

Since, scale inhibition is not appropriate for all conditions, due to the presence of hard minerals in the water.  Therefore, for water softening purpose, a process called Ion Exchange Method is generally recommended for areas where the alkalinity level of water is likely to exceed 180ppm, which is very hard water.

4. Ion Exchange Filters:

In these filters, ion exchange method is adopted to soften the hard water. In this method, magnesium and calcium minerals that are found in hard water are substituted with other ions i.e. sodium or hydrogen ions. Ion exchange method is better for various applications that maintain high temperature constantly. It is because the hard minerals present in the water are removed by ion exchange process physically, hence reducing the chances of lime scale.

5. Reverse Osmosis Filters:

These filters involve the process of reverse osmosis in which water is filtered through a semi permeable membrane with pressure to remove the impurities and other contaminants. In this process, pure water passes freely through the semi permeable membrane while the contaminants are captured behind. Reverse osmosis effectively removes the inorganic solid particles i.e. magnesium and calcium ions that are dissolved in the water.

The efficiency of reverse osmosis purification is incredible. Other filters are also used with reverseosmosis filters like mechanical or sediment filters and absorption or carbon activated filters.  Their combinations are installed to reduce the ratio of impurities and contaminants to the minimum level and provide better results in water purification.

In reverse osmosis purification, the pressure of water itself is utilized to force the water through the semipermeable membrane. Therefore, it does not need electric energy in the meanwhile. In different applications where maximum purity of water is demanded, reverse osmosis purification can effectively ensure 99.99% purity of the processed water.


Water filters work in a systematic manner to minimize the contaminants from water. There are different kinds of water filters that work specifically well in certain situations. The five most common filters along with their respective functioning mechanism have been highlighted. A combination of these filters is also installed in the water purification systems. It is because each and every kind of water filter has its own merits and demerits. Installing a combination can further improve the purity level of water and reduce the ratio of pollutants to its minimum. From the above discussion,you can easily select the kind of filter or a combination of these filters to install them for water purification system that is best suited for the required applications accordingly.

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