How Water Purifier Works: Step by Step Process

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Water Purifier Working Principle: Complete process of purification

Water purifier working principle

Before we understand how water purifier works, we should know how the water reaches our homes. We all know that the Earth is known as the blue planet because of the enormous amount of water it carries. But do you know out of which only 3 per cent is freshwater, and rest is saline water in the form of oceans? The freshwater is in the form of rivers, springs, groundwater and lakes. But this freshwater contains a lot of impurities which can cause serious diseases. Therefore, we need the best water purifiers to make it drinkable.

We use this freshwater for various purposes like drinking, washing, bathing, industrial uses, etc. Therefore, we need to ensure that the water we use is free from all the impurities. Before we understand, ‘How water purifier works’, let’s understand how water is treated before it reaches our homes.

Large scale water purification systems

Water purification systems
Large scale water purification systems

The freshwater from rivers and lakes are collected through pipes by the large water treatment plants for purification. In the first step, the water is stored in sedimentation tank for about 24 hours. Here, large solid particles settle down, and the water is passed to the second chamber.

In the second chamber, the addition of Alum takes place, which acts as a coagulant. Here small insoluble impurities settle down, and the water passes to the third chamber.

In the third chamber process of filtration takes place. In this step, the water passes through sand, charcoal and gravel. Most of the suspended impurities are removed in this process. Then the water passes to the next tank.

Water from the filtration chamber transferred to the Aeration chamber where air passes through water with the help of air diffusers. In this process, the taste and odour causing substances in water reduces.

Then the water is carried to the disinfectant tank. In this tank, the addition of chlorine takes place, which acts as a disinfectant. Oxidizing agents like Potassium Permanganate and Ozone also added to the water. Finally, the clean water supplied to the nearby water tanks.

Water Purifier Working Principle: Step by Step Explanation

There are a lot of diseases caused by drinking impure water. Therefore, a water purifier is a must for every household. You might wonder how water purifier works. In this article, we have discussed the water purifier working principle.

The water purifier we use at our homes work on the principle of reverse osmosis, and therefore generally known as RO water purifier. Reverse osmosis is the process where water passes through a semi-permeable membrane, which only allows water molecules to pass through it. This membrane stops all kinds of particles which are not visible by naked eyes, such as harmful chemicals and contaminants like pesticides, bacteria, viruses, microorganisms, ions, and even dissolved chemicals.

In most of the water purifiers, there are seven steps followed to purify the water.

Water Purifier Working Principle
How Water Purifier Works- step by step process

Step 1: Pre-Sediment Filter

You might have seen a filter installed adjacent to the water purifier. This filter is known as a pre-sediment filter. It removes all the particulate impurities from the water. Water is filled in the filter even if the machine is off. This filter improves the life of the pre-Carbon filter.

Step 2: Pre-Carbon Filter

Granular activated carbon is used in the pre-Carbon filter. It removes chlorine and all the organic impurities like pesticides, microorganisms, viruses, bacteria, etc. from the water. It also absorbs the compounds that cause bad taste and smell from the water.

Step 3: Post Carbon Sediment Filter

The post-carbon sediment filter is optional, but most of the brands use this filter. It removes the remaining particular impurities such as dust. This filter helps to improve the life of the RO membrane.

Step 4: RO Membrane

The RO membrane removes dissolved salts, pesticides and heavy metals like arsenic, lead and mercury. This membrane also removes hardness and microorganism such as bacteria, virus, protozoa and cysts.

Step 5: TDS Modulator

Then the water passes through the TDS Modulator, which adds essential minerals to the water. It also enhances the taste of water.

Step 6: UV Reactor

The UV Reactor further kills bacteria, virus and pesticides present in water. It ensures to deliver safe water.

Step 7: Post RO Filter

It is the last stage of water purification before water goes into your glass. In this stage, the taste of water is further enhanced.

TDS of drinking water

So far, we have seen how water purifier works. Now let’s see what is TDS of water. The term TDS stands for Total Dissolved Solids. It is defined as the combination of organic and inorganic matter which passes through 2-micron filter. These dissolved solids include calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates. Among all the ions mentioned, some are good, and some are bad for human health. The dissolved calcium and magnesium leads to the hardness of the water. Low TDS of water ranges from 1-100 mg/L. Maximum TDS level can be around 1000mg/L.TDS level is also responsible for the taste of water. A lower level of TDS in water is not beneficial.

Water TDS chart

Here is a chart representing TDS level and water quality respectively.

TDS in mg/LWater Quality
Less than 100Poor (as it misses essential minerals)
100 to 300Excellent
300 to 600Good
600 to 900Fair
900 to 1200Poor
More than 1200Unacceptable
Water TDS Chart

How TDS controller works in water purifier

TDS of water can be controlled manually in the water purifier. Suppose the TDS of tap water is 600 mg/l. When this water enters the water purifier, it passes through some of the pre-filters. Before water reaches to the RO membrane, the water is subdivided into two streams. One of the streams goes to the RO membrane, and the other goes to the mineral cartridge.

Adjacent to mineral cartridge there is a valve. This valve can increase or decrease the flow of water in the mineral cartridge. If more water flows from the mineral cartridge, it will increase the TDS and vice-versa.

The water form RO membrane and mineral cartridge mixes and passed to the next filter, which is generally UV Reactor. And this is how TDS controller works in the water purifier.


Water is important for every living organism to survive. 70% of the Earth is covered by water. But only very little water is consumable. We cannot directly consume water from rivers or lakes because lots of impurities are present in it. Therefore, we need a water purifier to make water drinkable. This article describes how water purifier works. We have discussed the journey of water from its source to our glass.

Q. What are the main impurities found in water?

There are a lot of impurities found in water which is broadly divided into two categories.

  • Insoluble impurities: These are in the form of particles, and they do not dissolve in water. Some examples of insoluble impurities are mud, dust, sand, bacteria, viruses, etc.
  • Soluble impurities: These are soluble substances which are present in water. The main constituent of soluble impurities are heavy metals salts such as lead, mercury, copper, cadmium, some dissolved pesticides, arsenic, fluoride, etc.

Q.  Why RO water tastes different?

RO water tastes bitter because of the dissolved carbon dioxide. It makes the water a little alkaline and maintains its pH value.

Q. What is the main disadvantage of water purifier?

The main disadvantage of water purifier is that a lot of water is wasted in the purification process.

Thank You for taking out your precious time to read our article. I hope it benefits you in some way. We would love to read your valuable opinions and highly appreciate any new suggestions. So please leave your comments below.

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