Water Purifier Buying Guide [ How To Choose The Best Water Filter]

Water is life; Like air, we can not live without water. We always care about breathing fresh and pure air. But do we care about drinking pure water?

God has gifted free pure water to every human being. But we are polluting water either intentionally or un-intentionally at a very alarming rate.

Industries are growing at a vast scale. Waste chemicals from sectors are going to the river and thus polluting it. The same water is coming into our home.

Can you imagine how much damage this type of water can cause to our health? Millions of people are dying every year in the world due to water-related diseases.

Nowadays, getting pure water is a privilege. Governments are trying their best to deliver pure water by processing it in plants, but those efforts are still insufficient for developing countries like India.

So what can we do? Can we afford to drink dirty water? Of course NOT. That is why having a water purifier is very important. Some people would say that we are getting groundwater. Why do we need a water purifier?

But the fact is that even the groundwater can have deadly pathogens like viruses, bacteria, or other toxic substances. So purifying the water using a water purifier makes a lot of sense.

Water Purifier
Water Purifier

The water purifier market is very saturated. Now and then, new technologies are evolving, and so are the variants.

You will be damn confused when you go to the market to buy a water purifier. With so many technologies and so many models, it isn’t easy to judge which one is the best.

That is why we are here to give you detailed guidelines about choosing a water purifier, what features you should look for in a water purifier, and so many other details.

So in this Water Purifier Buying Guide, we will talk about different features and technologies used in water purifiers so that you are informed enough to make a proper purchase decision.

After reading this article, you will learn about the following stuff.

  • What is a water purifier?
  • What is the cause of water pollution?
  • How does a water purifier work?
  • Different types of water purifiers.
  • Technologies used in water purifier
  • Comparison of different water purifier types
  • Best water purifier brands in India

Causes Of Water Pollution

Water is getting polluted due to many reasons. Some reasons are in our control, and some are not. Knowingly or unknowingly, many times, we pollute water and later pay for the price of consuming dirty water.

Water gets polluted when it comes in contact with harmful chemicals, industry waste, pathogens like viruses or bacteria, or other harmful substances. Do you know that even the fertilizers that we use in our backyard can cause water pollution?

Causes Of Water Pollution
Causes Of Water Pollution

In India, the main reason for water pollution is industrial waste, improper hygiene and excessive use of plastic, and the lack of awareness among the people regarding purified water. Below are some common reasons for water pollution.

  • Industrial waste
  • Marine waste
  • Sewage and wastewater
  • Oil leaks and spills
  • Agriculture
  • Radioactive waste
  • Global warming

Impurities in Water

Water is a great solvent. It can mix with anything, and when it is mixed with harmful substances, it gets polluted. Here are the impurities generally found in water.

  • Biological Contaminants
  • Chemical Contaminants
  • Physical Contaminants

Biological Contaminants

Biological contaminants include different viruses, bacteria, fungi, protozoa, and other deadly pathogens that pollute the water, which can cause fatal water-related diseases.

Often these pathogens can be removed when you boil the water as those pathogens can not survive high temperatures.

Chemical Contaminants

Chemical contaminants may include nitride, mercury, sulfur, or fluoride due to industrial waste or different other reasons. These chemicals are equally harmful like deadly pathogens and should be removed by the different filtration processes.

Physical Contaminants

Physical contaminants may include organic compounds like animal body materials, oil globules, and vegetables. Water may also include some inorganic contaminants like sand, clay, and eroded minerals.

What Is Totally Dissolved Solids ( TDS) In Water?

TDS means Totally Dissolved Solids that are present in the water. It can be inorganic or organic compounds present in the water in molecules, ions, or micro granular form.

Some solid that is present in the water are calcium, phosphates, sodium, potassium, nitrates, and chloride. It can also include mercury, lead, cadmium, arsenic, etc.

The normal filtration process can remove any particles that are more than 2 microns in size. To remove smaller particles, you need an advanced filtration process.

TDS In water
TDS In water

Even the water that we get from the processing plants may have a high TDS level because all processing plants use chemicals to purify the water.

And when that water passes through different pipes, contaminants from the pipe also dissolve into the water. So it is always better to again purify that water using a water filter before consumption.

The unit of TDS is milligrams per liter (mg/l). TDS is also measured in parts per million (PPM)

Drinking-Water TDS Chart

Drinking water TDS chart
Drinking water TDS chart
TDS ( mg/L)Rating ( Drinking)
50-150Excellent for drinking
> 1200Not suitable for drinking

Effects Of TDS On Water

High TDS in water can have the following effects. That is why it is always better to check the TDS level before use or consumption.

  • Change of taste
  • Change of odor
  • Change of color
  • Change of water hardness ( TDS greater than 150 is termed as hard water)
  • Harmful chemicals and pathogens

Types Of Water Purification Systems

There are different types of water purification systems based on the TDS level in the water. More TDS level means a more advanced purification system is required. Here are the different water purification systems available in the market.

  • Gravity Water Filter
  • Ultra Filtration Water Purifier ( UF)
  • Ultra Violet Water Purifier (UV)
  • Reverse Osmosis Water Purifier ( RO)

Gravity Water Filter/ Water Filter Pitchers

Most of us may remember that we used to use this type of water filter in the old days. There used to be two chambers. In the top chamber, we used to pour the water, and from the bottom chamber, we used to collect the purified water.

The top chamber has a water filter candle that filters out most of the visible contaminants. We need to replace that candle after a few months of usage as due to the accumulation of particles, that candle could no longer purify the dirty water.

Gravity water filter
Gravity water filter

The major issue with this type of water filter is that it can not filter out microscopic contaminants, which are also harmful to our bodies.

Generally, if the TDS level is less than 300, you can use this type of filter. Gravity filters do not need electricity.

Ultra Filtration Water Purifier ( UF Filter)

As the name suggests, Ultra Filtration water purification can filter out microscopic size particles. This type of water filter uses different permeable membrane filters to remove particles having sizes as small as 0.02 microns.

Ultrafiltration forces the water through the filters due to the hydrostatic pressure. Particles that have sizes greater than the membrane hole size are stuck to one side of the membrane, and on the other side, we get fresh water.

Schematic Of Ultra Filtration
Schematic Of Ultra Filtration

One of the main benefits of UF filters is that they can retain the minerals of water, but at the same time it removes harmful viruses and bacterias and anything that is not dissolved into the water. To remove the dissolved solids ( TDS), you need other modern filtration systems.

Capabilities of Ultrafiltration
Capabilities of Ultrafiltration
Credit: Freshwater systems

UF filter also does not change the taste of the water and does not use any electricity. That is why sometimes it is a preferred water filtration option for many.

Ultra Violet water Filter ( UV Filter)

UV filters use Ultraviolet radiation to kill harmful pathogens like viruses and bacteria but do not remove any chemicals or totally dissolved solids (TDS). UV filters do not add any chemicals and do not take away any minerals from the water.

UV filters only kill the germs but do not filter out those germs from the water. You still need other filtration systems to remove those dead germs. Otherwise, you will have to consume water with dead germs, which are still harmful to some extent.

Schematic of UV filtration system
Schematic of UV filtration system

One of the best parts of UV filters is that they consume very less energy (Equal to a 60 watts bulb) but can kill up to 99.99% of harmful waterborne microorganisms.

And the worst part is that UV filters alone can not give you 100% purified water. You need other filtration systems to remove the dead pathogens.

UV purifiers are not suitable for removing dissolved particles from the water. Some UV purifiers in the market use sediment prefilter and activated carbon filters to remove the high TDS value impurities.

Reverse Osmosis Purifiers (RO)

The full form of RO is reverse osmosis. It is one of the best and most advanced water filtration systems available on the market. But before we know about Reverse Osmosis, we need to learn about osmosis.

Osmosis Vs Reverse Osmosis
Osmosis Vs Reverse Osmosis

In the osmosis process, the water flow takes place from a lower concentration, i.e., low TDS value area, to a higher concentration area (high TDS value). Osmosis is a natural phenomenon, and that happens automatically.

Our kidney absorbs water from blood and trees absorbs water from the soil. There are numerous examples of the osmosis process.

Reverse Osmosis
Reverse Osmosis
Credit: Freshwater systems

Now, it’s easy to understand reverse osmosis. It is just the opposite of osmosis, i.e., the water flows from a higher concentration area to a lower concentration area with the help of external pressure.

Schematic Of Reverse Osmosis
Schematic Of Reverse Osmosis

The reverse osmosis process uses a semi-permeable membrane that allows water to pass through but stops the flow of harmful salt, bacteria, and other organics.

So in the case of RO water filtration, it can even remove the stuff dissolved into water. Other filtration systems can not remove totally dissolved solids.

To push water through the membrane, we need more pressure, and more pressure means more power. And to achieve more power we need an electrical power source.

Must read: RO vs UV vs UF – Which Water Purification Technology Is Best For You?

Difference Between RO Vs UV Vs UF

Requires ElectricityRequire ElectricityDoes not need any power source
Clean all germs and microorganismsCan kill germs but can not filter out thoseCleans most of the germs and microorganisms
Removes dissolved saltCan not remove dissolved saltCan not remove dissolved salt
Has prefiltrationNo prefiltrationNo prefiltration
Can clean dirty waterCan not clean dirty waterCan not clean dirty water
Use permeable membraneDo not use a permeable membraneUse permeable membranes of larger pores
Can reduce the TDS level up to 90%Does not reduce the TDS levelDoes not reduce the TDS level

RO+UV+UF Water Purifier Working principle

By now, you might have realized that if you want 100% purified and healthy water, then RO water filtration is the best. So it is wise to explain the working principle of a RO water purifier so that you have more knowledge about it and make the best purchase decision.

Schematic of RO Water Purifier Working principle
Schematic of RO Water Purifier Working principle

Here is a schematic of a RO+UV+UF water purifier system manufactured by Kent. Although the components may vary based on different manufacturers, the fundamental working principle remains the same.

Below are some of the common parts found in a RO+UV+UF water purifier and the kind of jobs they do.

Step-1: Pre-Filter or Sediment Filter

This is the first filter through which the water passes. Usually, a sediment filter is placed outside the RO system, and it can remove large particles like sand, soil, and other significant contaminants.

The working principle of a sediment filter is similar to a gravity water filter, but the only thing is that you need pressure for water to pass through this filter.

The sediment filter does a dual job here. It reduces the turbidity of water so that RO has less work to do, and it also reduces large impurities so that RO has fewer impurities to filter.

Step-2: Activated Carbon Filter

The next stage is the activated carbon filter stage. In this stage, the water coming out of the prefilter stage passes through the carbon filters, eliminating the organic impurities and bad odors present in the water.

Step-3: UF water filter

In this stage, the water coming out of the activated carbon filter is filtered again but with a membrane with hole sizes as small as 0.02 microns.

So a lot more ultra-small particles, pathogens, and other harmful substances are eliminated in this stage.

Step-4: RO Filter

After the carbon filter stage, RO filtration takes place. This is the vital stage in the entire purification process. The water that comes from the carbon filters passes through the RO filtration membrane.

RO membrane is made up of plastic filters. The holes are tiny, allowing the water molecules to pass through them quickly but stopping undissolved substances like arsenic, chlorine, and magnesium. So those impurities are removed from the water, and the TDS level is also reduced to an acceptable level.

Step-5: TDS controller / Mineraliser

After the water comes out of the RO systems, it loses minerals, and we know that minerals are required for healthy water. Water gets tasteless, too, after it comes out of the RO stage.

So a TDS controller/mineralizer replenishes the salt level in the water and balances the pH level so that the water becomes tasty and healthy again.

PH level of water
PH level of water

Step-6: Ultraviolet Filter

At this stage, the water passes through ultraviolet radiation that kills the remaining germs that escaped during ultrafiltration and the RO stage. However, the ultraviolet filter does not remove those pathogens from the water.

Step-7: Post Carbon Filter

The post Carbon filter is the last step in the RO purification process. The post-carbon filter then removes pathogens that were killed by the UV filter. Apart from that, any other impurities that were left out are also filtered out by this filter.

10 Key Factors To Consider While Buying A Water Purifier [ Water purifier buying guide]

Selecting the best water purifier is an intimidating task. Therefore, everyone must check certain things before buying them. Otherwise, you may end up at a loss. Here are the things that need to be considered.

  • Check the TDS level
  • Choose the type of filtration
  • The capacity of the water purifier
  • Electric or nonelectric
  • Alert System
  • Water waste
  • Installation and warranty
  • After-sales service
  • Brands
  • Budget

1. Check The TDS Level / Test The Water

Testing the tap water is mandatory if you are planning to have a water purifier. You can test the water using two methods. One is a manual check, and the other is using a TDS meter.

Natural testing of water involves the smell and taste of the water. If you find it smells terrible, It is enough to say that this water is not fit for consumption.

However, if you feel the water smells good, then it is not necessary that it is fit to drink directly. Then, what to do? You need to look at the color and sediments in the water.

Also, you can check the pipes whether it is corroded or not. If you find any of these problems, this is a sign that the water is not good enough to use and drink.

TDS Meter

Now if all the manual test is passed, still you can not be sure that the water is pure. So you need to test the water using a TDS meter to see if there are impurities that your manual testing could not catch. TDS meters do not cost much. You can get one for 100 bucks on Amazon.

If the TDS meter shows that the TDS level is below 300, you don’t need to buy a RO water purifier. Instead, you can buy a gravity system water purifier or a UF water filter.

But in case the value of TDS is more than 300 and less than 500, you need to get one RO-based water purifier for sure. If the TDS values cross 500, you should not consume that water even after purifying it through an RO water purifier.

2. Choose The Type Of Filtration

As we discussed, the type of water filter decision depends mostly on the TDS value of the water. If the TDS value is more, you have no option except to get a RO+UV+UF water purifier.

But even if your water TDS level is good, you can also opt for RO based water purifier to make sure that your drinking water is 100% pure.

3. Capacity Of Water Purifier

If you have a small family, then a 5-8 liter water purifier should be more than enough. But for a large family, anything above 10 liters of size is good, but you need to see the space availability.

All water purifiers come with a sensor that senses the water level. Whenever the water level goes below that threshold, the inlet valve opens, and water gets into the purifier for the purification process.

4. Electric or Non-Electric

Gravity water filters and UF water filters do not need electricity. So if your home has an electrical problem then it is better to for these water filters.

All RO water purifiers need electricity. Even if your area faces frequent power cuts, that may damage the RO water purifiers. So you need to consider that as well before buying one.

5. Alert System

The Alert system adds extra convenience to water purifiers. For example, when the purifier needs a cartridge change, it should sound an alarm or show a notification light.

When the water purifier needs service, it should give an alarm. If any of the systems are not working, then also it should give an alarm. So when you buy a water purifier, make sure it has sufficient alarm systems available.

6. Water Waste

RO water purifiers are known for wasting more water than other water purifiers. Some RO water purifiers waste as much as 3 liters of water to give one liter of pure water.

In areas where water is not readily available, you also need to consider this fact before buying a water purifier. Choose the one that wastes less amount of water.

7. Installation And Warranty

Installation of water purifiers is not as easy as a TV. It needs professionals to install it. Many times, companies won’t say upfront, but they will charge for installation and mounting brackets.

So when you buy a water purifier, make sure installation and mounting brackets are coming free of cost. Also, watch out for the warranty norms and exclusions to as not to face any issues later on.

8. After Sales Service

Unfortunately, most Indian brands are notorious for giving after-sales service. Once they install the water purifier, their job is done. Even if you raise a service request, they will take their sweet time to respond to it.

And when you raise a service request after the warranty is over, they will charge like a bomb for the service, and sometimes the cost of service is equal to the product cost itself. So before making a purchase, check if their after-sales support is good or not.

9. Brands

It would be best if you always go for reputed brands with a good reputation and portfolio in the market. If you buy a product from an unknown brand, you may get it for cheap, but you need to sacrifice the after-sales support. Here are some reputed water purifier brands in India


When it comes to water purifiers, Kent is a famous name that we can’t ignore. It is one of the best water purifier brands in India.

This brand is known for delivering high-quality and aesthetically designed water purifiers in the Indian market over a long period of time. If you want to have the best water purifiers, Kent is a great option for you because of its reputation and product quality.


Quality-wise, Eureka Forbes water purifiers are simply the best in the Indian market. It has been winning users’ hearts for almost 35 years. Starting from the beginning, the Eureka brand has been delivering quality water purifiers to Indian customers.

Today, Eureka is considered the top of all the leading water purifier brands in India because of its huge customer base.


HUL brand is known for manufacturing aesthetically pleasing water purifiers. Let me tell you; this is one of the brands which is well-known for its most advanced RO purifiers.

It features water purifiers with the newest state-of-the-art technologies like the 7 stages RO+UV+MF purification process to attain a maximum amount of pure water.


Havells is also becoming a big name in the water purifiers industry. If we talk about its history, this brand came into the Indian market a few years ago, yet it has established a name in the list of top water purifier brands.

This is because of its superior quality water purifiers and huge customer base. The Havells Max 7-liters RO+UV+Mineralizer is the masterpiece of its list of best Water Purifiers.

AO Smith

AO Smith is also a reputed name in the international market. But slowly, they have good footfall in the Indian market too. Although AO smith products are a bit costly, considering the kind of quality they offer, it justifies the price tag.

10. Budget

Water purifiers do not come for cheap. Good water purifiers with RO+UV+UF technology cost a minimum of 15000 INR.

So it’s better that you check the TDS level of water before investing in any RO water purifier. For example, if your water TDS level is less than 300, it does make sense to invest in RO water purifiers.

So your purchase decision should always align with your requirement. Otherwise, you will end up buying a product that you don’t even need.

RO water purifiers are the costliest followed by the UV and UF. And if you want RO+UV+UF, it will cost you the most.

Conclusion: Best Water Purifier Buying Guide

That’s all I have in this article. I hope now you have enough insights about different water purifiers and what kind of water purifier you should choose.

Having a good knowledge of the working principle and technologies used in a product gives you an edge when you go to the market to buy that product.

No salesperson can fool you because you know the in and out of it. I hope I could able to give you that level of knowledge about water purifiers through this article.

If you still feel that you want more knowledge about water purifiers or are stuck in your buying process, please let me know through the comment system, and I will be happy to help.

Frequently Asked Questions (FAQ) On Water Purifier Buying Guide

1. What is a TDS controller or modulator?

We know that the RO system reduces the TDS level in the water. RO systems also remove salts and other minerals from the water, which is essential for us. Without those salts and minerals, water will be tasteless.

To overcome this issue, many water purifiers come with a TDS controller. As the name suggests, it controls the TDS level of water.

In water purifiers with a TDS controller, not all the water goes through the RO system. A portion of water bypasses the RO system and goes through the UF filter.

UF filers are also good at removing pathogens and keeping the mineral level in the water. So in the TDS controller, it gets inputs from the RO system with a low TDS and from the UF system with a high TDS.

The resulting water from the TDS controller has an accepted range of TDS levels for proper taste and odor.

2. What is Mineralizer / Mineral guard

RO system removes almost all the minerals. The water that comes out of RO is pure without any taste.

That is why many manufacturers nowadays use a filter called Mineralizer or mineral guard that adds minerals to the purified water so that the water is pure and healthy too. Adding minerals also helps in maintaining a healthy PH level in the water.

3. How much electricity does a water purifier consume?

It depends on the type of water purifier you use. Gravity water purifiers and UF water purifier does not use electricity.

If you use a RO water purifier, then it consumes about 20-25 watts of electricity for average daily use. Here is the calculation of the annual power consumption of a RO water purifier.

Per day electricity consumption: 25 watts
Per year electricity consumption= 25×360= 9125 Watts=9125/1000~ 9 Units.

So a RO water purifier consumes about 9-10 units of electricity per year. If you use a RO+UV+UF, the electricity consumption will be more.

4. How much is the average annual maintenance cost (AMC) for an RO water purifier?

The annual maintenance cost depends on the brand. But on average, you may need to spend 3000-5000 per year for replacing the RO membrane, UF filters, carbon filters, etc.

Please note that you need to replace filters annually to get the best performance from water filters.

5. Can we use the rejected water from a water purifier?

We can not use rejected water for human consumption. But that does not mean that this water is a complete waste.

It is still 90-95% pure. You can use that water for gardening, washing clothes, or other similar kinds of stuff.

6. Which water purifier brand offers the best after-sales services?

That depends on the service availability of that particular brand. For example, the Kent water purifier is the best in terms of product quality and service. But if they don’t have any service center in your area, you will never get good service.

So before buying a water purifier from any brand, make sure you visit their website and see if they have any service centers in your area or not. Otherwise, look for other brands.

As per my personal choice, Kent is the best in terms of after-sales service.

7. What is the night assistance in a water purifier?

Night assist is nothing but LED illumination in a water purifier so that at night you can get pure water without really searching for it. It is more of a convenience feature rather than an essential feature.

8. How long we can keep water in a water purifier?

You can keep water in water purifiers for up to 2-3 days. Although the water is pure but water contamination gives birth to fungi and bacteria. So if you are going out for vacation, please make sure you clean in and out of the purifier before using it again.

9. When we should change the cartridge of a water filter?

It would be best to change it every year or whenever your cartridge life touches 90%, whichever comes fast.

All water purifier comes with a Cartridge End-of-the-life warning system. Watch out for that alarm and change it immediately.

10. What is the PH level of water?

pH is a measure of how acidic/alkaline water is. The range goes from 0 to 14, with seven being neutral. pHs of less than 7 indicate acidity, and greater than seven is alkaline.

Rajib Is The Founder And The Key Brain Behind RiansDeal. A NIT 2004 Graduate In Mechanical Engineering With Close To Two Decades Of Experience In Designing Large Appliances And Consumer Electronics Products.


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