How a Water Purifier Works

How a water purifier works? Here is some useful information that describes the working principle of a water purifier.

Every domesticwater purifierworks on the principle of removing the impurities by filtering the water with the help of membranes and killing the microbiological organisms in water by passing Ultraviolet radiation through the water. Though the manufacturers are also deploying some purifying agents and other technologies that add minerals to the purified water, these essentially may not be required every time. It all depends upon the source of water responsible for initial impurities and mineral contents in it.

The extent of impurities removal, post membrane, depends on the size of the holes on the membrane’s layer.

In some purification technologies, due to the removal of a significant quantity of total dissolved solids (TDS), the pH value of purified water falls towards the lower side of the desired limit range. It means that the purified water becomes slightly acidic. As the experts suggest that we should drink alkaline water, modern water purifiers are coming with an additional cartridge that increases the TDS level & PH level to the desired range, making it alkaline.

Now let us understand the sequence of “how a water purifier works,” i.e. the water flow sequence and the purification technologies that it passes through. 

how a water purifier works

The above illustration demonstrates “how a water purifier works” for a system that comes combined with all the three water purification technologies, i.e. the RO system, the UF system and the UV mode of disinfecting the biological impurities.

How a water Purifier Works – Stages

  1. The raw water (supply water) enters into the Pre-sediment filter, where it passes through a membrane with comparatively large holes and removes the solid particles in water.
  2. In the next step, the water passes through the inline sediment filter with small holes than the one in the pre-sediment filter stage. The pores size in sediment filter is, generally, 5 microns in size.
  3. In the third step, The water passes through carbon blocks (activated carbon). The carbon blocks are porous in structure and have excellent absorption properties. The pores in carbon blocks vary in size, usually from 1 nanometer to 25 nanometers, distributed un-uniformly throughout the carbon blocks. Macro impurities, along with the excess Chlorine in water gets removed here. Since the chlorine quantity in water is tapped-down here, the water improves in taste and odour.
  4. Now, in the fourth step, the water from the activated carbon chamber is sent in two directions
  • One pumped towards the RO membrane, and
  • Second, by gravity to the UF membrane

The flow of water towards UF is controlled by a TDS Controller/ TDS adjuster valve.

What is a TDS adjuster valve and Why is it used?

A TDS adjuster valve is a simple gate-type valve that regulates the flow precisely. The more water directed towards the UF membrane, the more is the TDS of purified water.

Let’s understand this:

RO membrane reduces the TDS contents of water by up to 90%. So the useful minerals( minerals essential for health), which come in the dissolved state, also get removed along with the other harmful dissolved solids. 

It means if the TDS content in your inlet water is 300 PPM, after passing through the RO membrane, it becomes as low as 30 PPM. It indicates very less presence of useful minerals in the water, which is, again, not suitable for our health, especially if consumed in the long run. 

 Now, water, when passed through the UF membrane, retains up to 40 % of minerals in the form of TDS, and you get around 120 PPM TDS in the outlet water. Together the outlet TDS content is maintained, and the purifier delivers the water that is more suitable to our health.

Note: In filtering the water through RO membranes, about 65% of the water passes out as wastage. It is a significant volume and can result in water wastage, hence it is recommended to store the wastewater and utilize it in activities like washing, gardening, etc.

  1. Though both the membranes can filter the microorganisms in the water, still, a UV chamber comes provided after these two purification membranes, that is in the 5th stage. The UV chamber kills pathogens, if any, in water. The pathogens may pass the filter membrane(RO and UF) if a rift occurs in the layer. There is a regulatory flow valve at the end of the UV chamber to reduce the flow rate inside the UV chamber, enabling the effective disinfection of germs in the water.
  2. The next step/ feature, found in some water purifiers, is the presence of an Alkaline cartridge.

The alkaline cartridge comes in water purifiers that use RO membrane to filter the water, and when the TDS controlling technique is not used. OR when even after using a TDS control valve, more alkaline water is desired. 

In this scenario, as 90% of TDS is filtered by the RO membrane, the pH of the outlet water shifts towards the low range of pH Level. (6.5 – 8.5 as recommended by BIS). This shift towards the lower side indicates the water is more acidic than alkaline. Though the water may remain under the limit, it is always advised by health experts to drink more alkaline water. 

In the 7th stage, the purified water gets collected in the storage tank. As soon as the storage tank gets filled, the float switch cuts the main supply and the solenoid valve closes, restricting the further supply of water in the sediment filter.

These are the basics of how a water purifier works.

How the Alkaline cartridges make the water Alkaline?

The Alkaline cartridges consist of a series of Ceramic balls that increase the TDS and PH of the water. Also, it comes loaded with activated carbon that enhances the taste of water.

Alkaline cartridge

The stages of ceramics usually found in an alkaline cartridge are as follows:

  • Negative ion balls
  • Alkaline balls
  • FRI Mineral balls
  • Anti-bacterial balls
  • Taste enhancer
  • Tourmaline balls
  • Silver Impregnated balls

The alkaline cartridges get exhausted after a certain period; once exhausted, you get the RO water. Different RO brands ask to change the alkaline cartridge after a specific period. We recommend keeping a TDS meter and a PH meter in your home, checking at regular intervals, and changing the cartridge accordingly. 


The above-illustration on “How a water purifier works” is a general-way that all water-purifiers for home acquire to purify the raw water. There can be additional elements to it, that modern water purifiers are coming with. Like the mineral cartridge or the Copper cartridge, the additional elements may not be your requirement if you are using municipal water or water from a source that does not offer much contamination. Among the many imperatives, we should achieve the goal of drinking pure water with recommended mineral content.

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