The Ultimate Guide for Buying A New Water Purifier

We’re pretty sure you’re convinced that every penny you spend on a great water purifier is a penny spent wisely, because of the health benefits of drinking purified and uncontaminated water.

Even apart from that, there are literally dozens of reasons for you to look for the best water purifier and get one home; for instance, water purifiers ensure:

  • Safety from life threatening waterborne diseases that may be caused by contaminated water
  • That the weird taste of chlorine, calcium carbonate is removed from tap water (which means it won’t spoil your coffee!)
  • Little to zero scratching, spotting, and scaling on the surface of your kitchen utensils.

This Water Purifier Buying Guide will help you identity the right water purifier for your home or office; read on.

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Before we discuss the different types of water purification technologies and which one out of these suits your needs, it is important to first understand the different types of impurities found commonly in drinking water. Because then only we’ll be able to understand the need for such varied types of water purifiers.

Different Types of Impurities Found Commonly in Drinking Water

The type of impurities found in the drinking water coming to your home mainly depend on the source and distribution medium of water. Most common sources of drinking water are: lakes, rivers, bore wells, harvested rain water, piped municipal corporation supply, water tankers etc.

The quality of water, level of impurities like harmful pollutants, chemicals and biological impurities like bacteria and viruses, and hardness, it all depends on the source of water.

Most common types of impurities in water:

Type of Impurity Most Common Water Source Effect on Drinking Water
Un-dissolved solids such as sand and mud River, bore well or piped water where pipes are damaged Muddy or turbid appearance
Dissolved inorganic salts like Sodium & Potassium Bore wells and seawater Salty or brackish taste
Dissolved inorganic compounds like Calcium & Magnesium Bore wells and river water Hardness and scale formation
Organic compounds Lakes and ponds Foul smell or bad odour
Decontaminants like Chlorine Municipal piped water supply Bitter taste
Biological impurities like bacteria & viruses Piped water where pipes are damaged, water tankers Biological contamination, waterborne diseases

Usually, water from lakes, rivers and harvested rain water will have a low TDS (Total Dissolved Solids) as compared to water from bore wells. Bore well or ground water generally has high TDS and may also contain harmful chemical impurities like lead, arsenic, etc. Piped water supply or water stored in tanks is generally more prone to biological contamination (if the pipes are damaged or the storage tanks are not cleaned frequently).

Identify the Water Type – Soft or Hard Water

Water can be classified as soft or hard based on the level of dissolved solids in water. Total Dissolved Solids (TDS) is regarded as the degree of hardness and is measured in units of Parts Per Million (PPM) or Milligrams per Litre (mg/L).

1 ppm = 1 mg/L

Water with TDS value ranging between 150-300 ppm is considered to be soft water, while water with TDS value higher than 500 ppm is considered to be hard or contaminated water.

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Hard and Soft Water

What’s the source of the water you get supplied to your home? If it comes from underground water, supplied by water tankers, or drawn from deep dug bore wells, then most probably it’s hard water. Now, hard water contains pretty high percentages of dissolved solids like calcium, magnesium, heavy metals, fluorides, and arsenic. All these dissolved impurities make hard water unfit for human drinking. On the other hand, water sourced from rivers, rain water harvesting systems, lakes, and municipality managed storage and delivery system is generally termed as soft water. Soft water, though not as dangerous, also needs purification before it can be deemed safe for human consumption over the long run.

Water Purifier Types, and Mapping them to Your Water Type

1. Reverse Osmosis (RO) Purifiers
To understand the working of RO, we need to first understand what Osmosis is.

Osmosis Process

In the normal osmosis process, the water naturally flows from an area of low solute concentration (low TDS level), through a membrane, to an area of high solute concentration (high TDS level). The pores of the membrane are very small (about 0.0001 microns), water molecules being smaller are allowed to pass through and the smallest dissolved impurities and bacteria are trapped.

As the name suggests, Reverse Osmosis (RO) does the opposite of Osmosis, that is, push the water molecules from the region of higher TDS level to the region of lower TDS level. This is achieved by applying an external pressure with the help of a water pump to reverse the natural flow of water. Water with impurities or high TDS is pumped at high pressure into the RO chamber, this pushes the water molecules across the semi-permeable membrane to the other side while leaving the dissolved solids and other impurities behind. All the dissolved solids and impurities along with some input water, also known as RO waste water, are discharged through a separate outlet.

Reverse Osmosis Process

RO purifiers are therefore always recommended for purifying water which has high TDS level. The TDS level of the output drinking water from RO purifier is very low as compared to the input water.

Some drawbacks of RO technology:
Requires Electricity: A high pressure electrical water pump is used to apply external pressure on the input water, hence RO purifiers cannot work without electricity.
Wastes Water: A significant part of the input water is discharged along with the dissolved impurities, which results in unnecessary wastage of water. On an average, RO purifiers produce 3 litres of waste water for every 1 litre of purified water.

2. Ultrafiltration (UF)
Like RO, Ultrafiltration also uses a semi-permeable membrane to purify water. After reading the first sentence, you must now be thinking if both RO and UF use the same method to purify the water then what is the difference between RO and UF. Ultrafiltration or UF uses a membrane with much larger pores (appx. 0.01 microns) as compared to RO which uses a membrane with very small pores (appx. 0.0001 microns).


The advantage of using Ultrafiltration is UF purifiers can work without electricity because the membrane has much larger pores and water can pass through it naturally using the force of gravity. Which means no external pressure or water pump is required. Also, since UF purifiers do not hold back any water, there is no wastage of water.

But there are some limitations of using UF purifiers, because of larger pore size, UF can only remove un-dissolved solids and larger impurities. It cannot remove the dissolved solids or reduce the TDS level. So, UF purifiers are not suitable for purification of high TDS water or hard water.

RO UF Comparison

3. Ultraviolet (UV) Purification
As the name suggests, Ultraviolet or UV purification uses ultraviolet rays for the purification of water. A UV purifier works by throwing high intensity UV rays on the water which kills or inactivates the disease causing bacteria and viruses.

However, UV purifiers cannot remove any dissolved or un-dissolved impurities or chemicals from water. Because of which most of the UV purifiers that are available in the market use some form of external sediment pre-filters to remove un-dissolved impurities and activated carbon filter to remove Chlorine and some dissolved impurities.

Therefore, UV water purifiers are only recommended for areas where the water source has low level of TDS.

If the water has low TDS level but it is contaminated with bacteria and viruses and appears muddy then you can use UF+UV water purifier.

4. Tap/Faucet Mounted Filters or Gravity Based Purifiers
These types of filters or purifiers are simplest to use and provide the most basic water purification. These filters generally comprise of sediment or sediment + activated carbon filters which can remove large and un-dissolved impurities like mud and sand along with some chemicals and microorganisms. Tap/Faucet Filters are very small in size and can be directly fitted on taps.

Tap/Faucet Filter and Gravity Based Purifier

Gravity based storage purifiers are the advanced version of tap/faucet filters. These purifiers offer slightly advanced purification and come with in-built storage tank to store input/impure water. Most of the Gravity based water purifiers available in Indian market now have 2 separate storage tanks for input/impure and output/purified water.

Tap/Faucet Mounted Filters and Gravity Based Purifiers are only suitable for areas where TDS level is low and water is not highly contaminated with biological impurities like bacteria, viruses and other disease causing germs.

Which Water Purifier Should I Choose?

RO technology has become synonymous with water purifiers and you must have heard a lot of people referring to water purifier as RO (like the brand Xerox has become synonymous with photocopying).

Because of this, when we talk about buying a water purifier most people think RO water purifiers should be purchased by default without considering the most important facts like the source of water and TDS level of input water.

If you have read all the above discussion then you are well aware of the fact that RO purification is required only when the water coming to your home or office has high TDS value (generally higher that 300 ppm).

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You may also like to read the difference between RO vs UV vs UF.

These days there are different kinds of water purifiers available in the market ranging from simple tap/faucet filters and Gravity based purifiers to UF, UV, RO and their combinations. This vast range of different technologies and thousands of different water purifier models from tens and hundreds of brands have increased the complexity of buying the right purifier for your home or office.

As discussed earlier, you should buy a RO purifier only if the water to be purified has a high TDS level. The Bureau of Indian Standards (BIS) has specified the maximum TDS limit for safe drinking water as 500 ppm. But to be on safer side, we recommend opting for a RO purifier if the TDS level is higher than 300 ppm.

There is absolutely no need to use a RO purifier if the TDS level is below 300 ppm. Because if your water source has low TDS then the RO purifier will further reduce it to a very low TDS level. Which means the purified water will then be devoid of essential minerals like calcium and magnesium which are required for our good health.

If the TDS level of incoming water is below 300 ppm then you should check the incoming water for turbidity (clarity), muddy appearance, or presence of biological impurities like bacteria and viruses.

Though water purifier makers try to differentiate their products from competitors by flaunting advanced water purification technologies, most of them actually use a mix of three major purification approaches – reverse osmosis (RO), ultraviolet (UV), and UF (ultra filtration).

If you do not want to go into the technicalities of the different purification approaches, then you can simply refer to the below given, easy to remember, checklist that helps you buy the right purifier for your home or office. Here we will list all the parameters to evaluate and choose the right water purifier according to your needs.

TDS Level Is Water Muddy? Presence of Biological Impurities? Ideal Choice
Below 300 ppm No No Gravity Based Purifiers
Below 300 ppm No Yes UV
Below 300 ppm Yes No UF
Below 300 ppm Yes Yes UF or UF+UV
Over 300 ppm No No RO
Over 300 ppm No Yes RO+UV
Over 300 ppm Yes No RO+UF or RO+UV+UF
Over 300 ppm Yes Yes RO+UV+UF

  • Soft water has low TDS level; UF water purifiers work pretty well for it.
  • For soft water with high level of biological contamination, go for a UV or UF+UV water purifier.
  • Hard water contains higher level of TDS, apart from specific toxins; so, RO based purifiers are well suited for purifying it.
  • For hard water with high level of biological contamination, go for a RO+UV or RO+UV+UF water purifier.
  • UF filters are best used in combination with another water purification system, as they don’t kill any microorganisms in contaminated water. UF filters only remove suspended solids from water.
  • Activated carbon based water purifiers are ideally suited to remove excess chlorine from water.

Main Components of RO Water Purifier

  • Sediment Pre-filter: In the first stage of purification, the input water is filtered using a pre-sediment filter. Pre-sediment filter not only removes fine and coarse particulate impurities/dirt but also improves the life of the RO/UF membrane resulting in lower cost of maintenance. If the purifier does not include this as a standard feature then it can be added separately as well.
  • Activated Carbon Pre-filter: Activated carbon pre-filter removes chlorine and organic impurities like harmful pesticides from the water. Activated carbon pre-filter also adsorbs bad odour and taste-causing organic compounds from water.
  • RO/UF membranes: Water is fed into RO membrane at high pressure using an in-built water pump. RO membrane removes the hardness, dissolved salts, pesticides and heavy metals like lead, arsenic and mercury. It also removes microbial contaminants like virus, bacteria, protozoa and cysts. The UF membrane also works like RO membrane but it does not remove the dissolved solids. Some purifiers use both RO and an UF membrane, the output water from both the membranes is mixed to control the TDS level of purified water.
  • TDS controller: TDS controller is used to control the TDS level of the output water. RO process not only removes bad impurities but also removes essential minerals like Calcium & Magnesium. TDS controller retains adequate quantities of essential minerals in the purified water by adjusting the ratio of water from RO membrane (low TDS) and UF membrane (normal TDS) in the final mix.
  • UV Filter: UV filter uses a high intensity UV bulb to kill or inactivate any virus, bacteria, and parasites to deliver safe water.
  • Carbon Post-filter: Carbon Post-filter acts as a polisher and enhances the taste of purified water. It also removes any foul smell from water.
  • Storage Tank: This stores the purified water for later use. Make sure the storage tank is made of food grade, non-toxic material. Some of the high end water purifiers now come with a stainless steel water storage tank. You should also check the capacity of storage tank.
  • Display: Most of the RO water purifiers come with basic display for purifier on/off, tank full etc. Some advanced purifiers also come with fault alert, membrane change, UV fail, TDS level indicator, purity indicator etc.

Gravity Based Water Purifiers – Where Do They Fit In?

Good question. Considering they’re inexpensive and effective, it’s natural that these filters excite a lot of interest, especially among first time buyers of water purifiers. Now, these filters don’t deliver advanced water purification capabilities such as that of RO and UV based filters. So, the only scenarios where they become practical options are:

  • When you don’t have optimum conditions for installation of an electric water purifier, such as optimum water pressure, electricity, and running water supply.
  • When you need to switch homes frequently and don’t want to have bulky equipment to move around, and re-install every time.
  • When you have a very limited budget.

In such situations, you could either choose to buy purified water in bulk from a convenience store, or install a gravity based water purifier.

Installation Feasibility of Water Purifiers

Most RO and UV based water purifiers are bulky and pretty heavy. Before you buy one, make sure you know of its dimensions, and have a plan to have it wall mounted in the kitchen area. You will need to provide an inlet for electricity, and another for water. Also, there must be continuous water supply at decent pressure, particularly when the water purifier is mounted high on a kitchen wall.

Reducing and Reusing RO Waste Water

An average RO purifier wastes approximately 3 litres of water for every 1 litre of purified water. That means only 25% of water is purified and 75% of water comes out as waste.


It’s true. This high percentage of water wastage is a major cause for worry. If you are also using a RO water purifier at your home or office then we request you to follow the below given tips to reduce the wastage of water and re-use the waste water generated by RO purifiers.

  • If the output water from your purifier has very low TDS (less than 150) then it means your purifier is generating more waste water. A very low level of TDS not only results in higher wastage of water but it is also bad for our health as it is devoid of essential minerals. Increasing the TDS will not only make the drinking water healthier but also reduce the wastage. You can increase the TDS level of your water purifier using the TDS controller knob.
  • Store and re-use the waste water.

Final Thoughts

The sole and biggest criteria to decide the type of water purifier you should buy is the source of water and the kind of impurities present in the water supplied to your home or office. Use the suggestions shared in this water purifier buying guide to buy a new water purifier for your home or office.

How to find best water purifier in India?

Hindi Video Tutorial for buying a new water purifier for home use in India.

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  1. This water purifier guide is awesome. Thank you for sharing this. I want decided to buy an RO and i think this solves my all problem even If i don’t know about the problems in my water supply. let me know if choosing an RO water purifier is good option or should i go with any other.

  2. The water coming to our home has a TDS of 170. Do I need to use an RO water purifier?

    • Since the TDS level of the input water is already very low, there is no need to use an RO purifier. You can opt for UV or UF or UV+UF water purifier.

  3. This is awesome guide. I have having a low TDS of 200 in hour home water supply. A gravity based water purifier is enough for us to make sure that we drink pure water. let me know.

  4. My drinking water is getting mixed with some amount of hard water (bore well water), due to faulty pipeline. The result is fluctuating TDS in range of 100 – 250 (without mixing, the municipal water has TDS < 50). We are trying to get the pipeline fixed, but meanwhile I plan to buy a purifier.

    1) I'm not sure what impurities are present in Borewell water. Should I get it tested? I plan to buy a TDS measuring device, but not sure if any other tests are needed. Pls advise.
    2) Considering bore well water, any suggestions if RO + UF is needed or only UF is fine?
    3) Do RO & UV purifiers retain the essential minerals in water? I'm especially doubtful about using UV purifiers. Whereas UF seems quite alright.

    Note that in past we have never used any purifier. We just used a clean cloth to filter water and we never had any issues,since municipal water quality was fine.

    • Please find point-wise replies to your queries below:

      1. The most common impurities found in bore well water is high TDS, mud/sand and heavy metals like lead and arsenic (quite rare). Even with mixed water the TDS which you have given is quite normal. However, it is always better to get your water thoroughly tested to find the kind of impurities present. You can also use this water test kit.
      2. Since the TDS is between the range of 100-250 you can go for UF purifiers.
      3. There is no loss of minerals in case of UV purification because UV purification doesn’t filter your water it only kills/deactivates the harmful microorganisms like viruses and bacteria. Since the TDS of incoming water is quite normal, RO purifiers without mineralizer or TDS control may result in loss of essential minerals.

      The ideal choice in your case should be UV+UF purifier. If you want to go for a RO purifier make sure the RO purifier has mineralizer or TDS control feature.

  5. Ro water is really not good for drinking. Yes, it removes the impurity of water but also removes the minerals of water as mentioned above. We always aware of it while purchasing any water purifier. That the purifier is not only a Ro purifier but also check that it consists of technology for mineralizing the water. Such as the purifier gives the alkaline Ro water for drinking.

  6. How to find TDS level of water? If to be tested in lab, which lab? I live in Anna Nagar, Chennai. Or any easy method to test TDS level at home?

    • Please read our detailed article on How to Check TDS Level of Water?

      You can buy a TDS meter (available on all leading online stores like Amazon & Flipkart) to check the TDS level of water at your home. Using a TDS meter is as easy as finding your body temperature using a digital thermometer. You can also use this water test kit to find the level of 8 common impurities in just 10 minutes.

  7. I get municipal supply drinking water with 280<tds<300. I happen to have a spare RO filter (Magna) from Aquaguard. Kindly advise if I should install the same without any fear of virus/bacteria or should I go for a UV filter?

  8. Nice article, before buying water purifier we should check the water. We always aware about it before buying a water purifier. This article is very helpful for those people who are not able to decide which water purifier most suitable for them.

  9. we need to water purifier for home use

  10. am from kerala ,which water Purifier suits me as we are using water from own Well.

  11. Does AMC cover all consumables like a membrane, activated carbon, UF and mineralization additives, and UV bulb?
    If KENT or any other good quality water purifier is bought online who arranges installation and aftersales service and AMC?

    • All reputed brands provide free installation when you buy online from reputed online stores like Amazon and Flipkart.

      All good brands’ purifiers are covered under manufacturer warranty, so the brands provide complete customer support and after-sales service.

      Regarding AMC, it is not the part of the initial purchase. You can buy AMC packages once the purifier is installed. Every brand has different AMC packages.

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