RO, UV, UF and TDS in Water Purifiers: A Simple Guide

RO, UV, UF, and TDS are four distinct technologies that address different water quality problems, and the right purifier for your home depends entirely on your water source's TDS (Total Dissolved Solids) level. Test your water first: above 300 ppm (typical of borewell or tanker water) needs RO plus UV plus UF; below 200 ppm (typical of treated municipal supply) is adequately served by UV plus UF alone, at a lower cost and with no water wastage.

• RO (Reverse Osmosis): Removes dissolved salts, heavy metals, fluoride, and arsenic by forcing water through a semi-permeable membrane; rejects 3–4 litres of water per litre purified; essential for water above 500 ppm TDS
• UV (Ultraviolet): Kills up to 99.99% of bacteria and viruses using light, with no chemicals and no water wastage; does not remove dissolved salts or TDS
• UF (Ultrafiltration): Filters fine particles, bacteria, and cysts through a membrane using only water pressure, no electricity required; does not remove dissolved salts or TDS
• TDS controller: Not a filter — a bypass valve that blends a portion of pre-filtered water back into RO output, raising TDS from near-zero to a palatable 50–150 ppm
• Decision rule: TDS above 300 ppm → RO+UV+UF; TDS below 200 ppm → UV+UF is sufficient and more economical
• Test your water first: A basic TDS meter costs Rs. 200–Rs. 500 and gives an instant reading that determines your purifier category

You can buy water purifiers of every technology combination on Easy EMIs at over 1.5 lakh partner stores across 4,000 cities, including Reliance Digital, Croma, and Vijay Sales.

Walking into a store and choosing a water purifier based on price or brand alone often means buying the wrong technology for your specific water source — paying for RO filtration you do not need, or worse, buying a UV-only purifier that cannot remove the dissolved salts in your borewell water. Understanding what each acronym actually does, and testing your water's TDS level before you shop, takes less than five minutes and ensures you buy the right system the first time. This guide explains all four technologies and gives you a clear decision rule based on your water source.

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Modern water purifiers use four main technologies to make drinking water safe, and each one addresses a different category of impurity found in Indian water sources.

• RO (Reverse Osmosis) removes dissolved salts and heavy metals by forcing water through a semi-permeable membrane under pressure.
• UV (Ultraviolet) kills bacteria and viruses using ultraviolet light, without removing any dissolved minerals or salts.
• UF (Ultrafiltration) filters fine particles and microorganisms through a membrane with microscopic pores, working entirely on water pressure without electricity.
• TDS control is not a filtration stage at all — it is a bypass valve that blends a small portion of pre-filtered water back into RO output, helping retain healthy minerals and natural taste after RO purification.

Knowing how each method works — and critically, what each one does not do — makes it straightforward to choose the right purifier for your specific water source and household needs, rather than over-paying for technology you don't need or under-purifying water that requires more thorough treatment.

Each purification technology works through a different physical process and addresses a different category of contamination. The table below sets out the working principle, what each technology removes, what it leaves untouched, and the water wastage associated with it — the four facts you need to compare technologies meaningfully.

The pattern in this table is the key insight: Only RO addresses dissolved salts, heavy metals, fluoride, and arsenic. UV and UF are both excellent for biological contamination (bacteria, viruses) but neither touches dissolved solids. This is why your water's TDS level — not your budget or brand preference — should be the first factor determining which technology you need.

Each technology offers a specific benefit, and combining them creates a more comprehensive purification system than relying on any single technology alone.

• RO delivers the most thorough purification for high-TDS water: In areas where borewell or tanker water has a TDS level above 500 ppm, RO is the only technology capable of bringing dissolved salts, heavy metals, fluoride, and arsenic down to safe drinking levels. Municipal water alone cannot guarantee consistent TDS safety across all areas, making RO essential for most urban and semi-urban Indian households relying on groundwater sources.
• UV provides fast and chemical-free disinfection: UV purification kills up to 99.99% of bacteria, viruses, and other pathogens without using any chemicals, iodine, or chlorine. It is particularly valuable as a secondary disinfection stage after RO, ensuring any microorganism that might pass through the membrane is completely neutralised before the water is dispensed.
• UF offers effective filtration without electricity: UF membranes work entirely on water pressure without requiring any power source, making them ideal for areas with frequent power cuts, or as a standalone solution for households with municipally treated water that has low TDS but may contain fine suspended particles.
• TDS control preserves the natural taste of water: Pure RO water with very low output TDS can taste flat and slightly acidic because nearly all mineral content has been removed. A TDS controller blends a small portion of filtered water back into the RO output to maintain a TDS level of 50 to 150 ppm — the range most people find naturally palatable, while retaining beneficial minerals like calcium and magnesium.
• Combined RO and UV provides complete protection: Pairing RO with UV creates a system that handles chemical and biological contamination simultaneously, delivering protection that neither technology achieves independently. This combination is the standard recommendation for most Indian households where water source quality cannot be guaranteed consistently.

The table below compares all four technologies side by side across the parameters that matter most for choosing between them, including a generic cost range by technology category.

Choosing correctly starts with one simple step: testing your water's TDS level before comparing any purifier models. The five-point guide below walks you through the full decision process.

• Test your water TDS level before buying: A basic TDS meter, available for Rs. 200 to Rs. 500, tells you the dissolved solids level in your tap water within seconds. This single reading determines whether you need RO purification or whether UV and UF alone are sufficient for your household — and it is the single most important purchasing decision you will make in this entire process.
• Choose RO plus UV plus UF if your water TDS is above 300 ppm: For borewell water, tanker water, or areas with hard water, a multi-stage RO plus UV plus UF system is the most comprehensive and recommended choice. The RO membrane handles dissolved contaminants, UV provides biological disinfection, and UF polishes the water before dispensing.
• Choose UV plus UF for municipally treated water with low TDS: If your water is supplied by the municipal corporation and has a TDS below 200 ppm, a UV plus UF purifier is sufficient and considerably more economical than an RO system. It kills pathogens, filters fine particles, and wastes no water during the purification process.
• Always include a TDS controller if you are buying an RO system: RO water with a very low output TDS can taste flat and lacks essential minerals. A built-in TDS controller maintains the output TDS at a natural, palatable level, improving taste and retaining beneficial calcium and magnesium important for everyday health.
• Check the purification capacity against your daily requirement: Most household water purifiers purify 10 to 20 litres per hour. For a family of four using approximately 15 to 20 litres of drinking water daily, a purifier with a 10–15 litre storage tank and 15 litres-per-hour purification capacity is adequate for uninterrupted supply throughout the day.

The table below maps specific purifier models to their RO/UV/UF/TDS configuration, helping you compare actual products:

Disclaimer: Each model's features, availability, and pricing are subject to change and may vary. For the most accurate and up-to-date information, please visit the official website.

Before you decide, explore the latest offers. You may find a great deal on a model that matches your needs.

Bajaj Finance offers two financing options for purchasing water purifiers. Both options are available at over 1.5 lakh partner stores across 4,000 cities in India, including Croma, Reliance Digital and Vijay Sales.

How to choose: Both options require you to be physically present at a partner store. The Insta EMI Card suits buyers who purchase across multiple categories over time. The Easy EMI Loan is better suited for a single water purifier purchase in one transaction. A minimum CIBIL score of 650 is required for both options.

The process is simple and typically takes 10 to 15 minutes once you are at the store.

1. Browse water purifier models on Bajaj Mall: Compare models by purification technology (RO, UV, UF), storage capacity, and price before visiting a store. Check your water source TDS level if known. Most municipal water in India ranges from 100–300 ppm, while borewell and tanker water can range from 500–2,000 ppm.
2. Find a partner store near you: Use the Bajaj Finance store locator to find the nearest Reliance Digital, Croma, Vijay Sales, or any of the 1.5 lakh partner outlets across 4,000 cities.
3. Check the purifier in person: Confirm the purification technology matches your water source (RO for borewell/tanker/high-TDS; UV or UV+UF acceptable for low-TDS municipal supply); verify the storage capacity suits your household size; ask about filter replacement frequency and AMC costs for the specific model.
4. Choose a suitable EMI option: Ask the store representative about the Bajaj Finance Insta EMI Card (pre-approved limit up to Rs. 3 lakh) or the Bajaj Finance Easy EMI Loan (up to Rs. 5 lakh). Both offer tenures of up to 60 months with zero down payment on select models.
5. Complete payment and take your water purifier home: The in-store process is quick, and most models are available for same-day pickup or scheduled installation.

You can also check your loan eligibility online in advance by entering your mobile number and OTP, helping you plan your purchase better before visiting the store.

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