Most people buy a water purifier the way they buy an umbrella in a downpour, in a panic, from whoever is standing in front of them, based on whatever the salesperson says. Then six months later the water still tastes off, the filters cost a fortune, and nobody can explain what the machine actually removes. After 15 years running my own borewell, pump and overhead-tank setup, I have watched neighbours make this exact mistake again and again. A simple water treatment buying checklist is the fix: it turns a confusing, high-pressure purchase into a calm tick-box exercise.
In this post I will hand you the exact checklist I wish I had when I started, from reading your test report, to sizing for flow, to pinning down running costs and the questions that make a dealer squirm. Print it, fill it in, and you will walk into any showroom knowing more than most people who work there.
Key Takeaways
- Test first, shop second. A lab report for under ₹1,500 tells you what to remove; buying blind wastes far more than that.
- Match the system to your peak flow, a whole-house unit that chokes below 15-20 litres per minute will annoy you every single morning.
- Compare the 5-year running cost, not the sticker price. Filter and membrane changes often cost more than the machine over its life.
- A good buying checklist covers six areas: test results, flow and pressure, budget, maintenance, warranty, and dealer questions.
- For anything touching drinking-water safety, confirm your numbers with a certified lab, never rely on a dealer’s free “TDS demo” alone.
Why a buying checklist beats a sales pitch
A water treatment system is one of the few home purchases where the seller knows vastly more than the buyer, and where the “problem” is often invisible. That imbalance is why a written water filter shopping checklist matters. Arrive with your own numbers and the conversation flips: instead of being sold a machine, you are matching one to a spec you already defined.
The other reason is money. The expensive mistakes are rarely the ₹8,000 you overpay upfront, they are the wrong technology entirely, like a fancy RO unit installed on water that only needed a sediment filter. If you have not yet worked out which technology your home needs, start with our complete guide to choosing the right water treatment system, then come back here to lock in the purchase.
Section 1: Your water test results
This is the section everyone wants to skip and nobody should. Treatment is chemistry, and you cannot pick the right chemistry without knowing what is in your water. A basic lab panel in India typically runs ₹800, ₹1,500; a broader one with metals and pesticides more. Before you spend anything on hardware, get these numbers on paper.
- TDS (total dissolved solids), the headline number, but never the whole story.
- Hardness (calcium and magnesium), decides if you need a softener.
- Iron and manganese, the staining and metallic-taste culprits.
- Bacteria / coliform, decides if you need UV or chlorination.
- pH, very acidic or alkaline water changes what equipment can survive.
- Nitrate, fluoride, arsenic, health-critical, and each needs specific treatment.
If you are unsure how often to run this panel or where to send a sample, the World Health Organization publishes plain-language guidance on drinking-water quality, and India’s Bureau of Indian Standards sets the IS 10500 limits your lab will compare against. Do not treat a dealer’s free “TDS pen” demo as a test, it measures one thing and tells you nothing about bacteria, iron or nitrate.
Safety note: If your report flags bacteria, arsenic, nitrate or fluoride above the limit, that is a health matter, not a taste preference. Do not self-prescribe a filter from a chart. Confirm the result with a certified lab and, where health contaminants are involved, get advice from a qualified water professional before you drink the water.
Section 2: Flow, pressure and where it goes
A filter that cleans water beautifully but slows it to a dribble is a filter you will grow to hate. This is where a water system requirements template earns its keep, you write down what your home actually demands before anyone quotes you a box.
Point-of-use or whole-house?
Point-of-use (POU) sits under one tap, usually the kitchen, and treats only drinking and cooking water. Point-of-entry (POE), or whole-house, treats everything as it enters the home. The right answer depends on your test report: bacteria and taste problems can often be handled at the kitchen tap, while sediment, hardness and iron that damage plumbing and geysers usually belong at the whole-house stage.
Sizing for peak flow
Size a whole-house system for your peak demand, not your average. Add up the fixtures likely to run at once, two showers and a tap during the morning rush is a realistic worst case. As a rough guide, each fixture pulls roughly 6-12 litres per minute. On my own borewell line I sized the sediment stage for about 20 litres per minute so the pressure never sags when the household wakes up at once.
| Household size | Typical peak flow | Whole-house filter port | Notes |
|---|---|---|---|
| 1-2 people | 8-15 LPM | ¾” ports | Slim housings usually fine |
| 3-4 people | 15-25 LPM | 1″ ports, Big Blue housing | The common family sweet spot |
| 5+ / large home | 25-40 LPM | 1″, 1¼”, twin or triple housing | Consider parallel filters to avoid pressure drop |
Also write down your line pressure. Many RO and UV units want a minimum working pressure (often around 1-3 bar). If your gravity-fed overhead tank cannot supply that, you may need a booster pump, a cost the dealer rarely mentions until after you have signed.
Section 3: Budget, sticker price versus 5-year cost
The single biggest budgeting mistake is comparing purchase prices. The number that actually hits your wallet is the total cost of ownership over five years: the machine, plus filters, plus membranes, plus electricity, plus service visits. A cheap unit with expensive proprietary cartridges can quietly cost more than a pricier one with standard parts.
| Cost line | Typical range (India) | How often | Watch out for |
|---|---|---|---|
| Sediment / pre-filter cartridge | ₹150, ₹600 | Every 2-6 months | Faster in muddy borewell water |
| Carbon / activated block | ₹300, ₹1,200 | Every 6-12 months | Proprietary vs standard sizes |
| RO membrane | ₹1,200, ₹3,500 | Every 2-4 years | Shorter life on hard/high-TDS water |
| UV lamp | ₹600, ₹1,800 | Yearly | Easy to forget until it fails silently |
| Annual service (AMC) | ₹1,000, ₹3,500/yr | Yearly | Check what is actually included |
Ranges vary with your water quality and local labour, so treat these as planning figures, not quotes. For a full breakdown of what systems cost upfront and how long they take to pay back, our deep dive on what a home water treatment system really costs works through the maths with real examples.
Tip: Before you buy, ask the dealer to write down the exact part number and price of every consumable, and whether it uses standard or proprietary cartridges. On one unit I nearly bought, the “cheap” machine used a locked-in filter that cost triple the generic equivalent. Standard 10-inch cartridges are your friend; they are cheap and available anywhere.
Section 4: Maintenance and warranty
Every treatment system is a commitment, not a one-time buy. A filter that is never changed becomes a breeding ground and can make your water worse than no filter at all. So your checklist has to cover who does the work, how easy it is, and what happens when something breaks.
- Can I change filters myself? DIY-serviceable units with standard cartridges save thousands over their life.
- Are spares available locally, or do they ship only from the brand?
- Is there a filter-change indicator, or do I need to track dates myself?
- Warranty length and scope, does it cover the membrane and electronics, or just the plastic housing?
- Response time for service, a week without a working UV lamp is a week of boiling water.
Sediment stages are the one part most owners can and should handle themselves. If you want to see how simple it is, our walkthrough on installing a whole-house sediment filter yourself shows the whole job, and it doubles the life of everything downstream.
Section 5: Questions to ask the dealer
Here is the before buying a purifier list of questions I ask, in order. Any dealer worth buying from will answer them without deflecting. Watch how they respond, a good one reaches for your test report; a weak one reaches for the TDS pen.
- Which specific contaminants in my test report does this system remove, and to what level?
- Is this technology overkill or under-spec for my numbers?
- What is the flow rate under my actual line pressure, not the lab-perfect figure?
- What does a full set of consumables cost per year, by part?
- Are the cartridges standard or proprietary?
- What does the warranty cover, and who handles service, you or a distant call centre?
- How much water does an RO unit waste per litre produced?
- Can I see this exact model installed somewhere nearby?
If a dealer cannot answer question one without first testing your water, that is a good sign, it means they treat the report as the starting point, the way you now do.
Section 6: Your copy-and-use checklist
Here is the whole filtration decision checklist in one place. Copy it into a note or print it, tick each item, and do not commit until every box is filled. This is the template I hand friends before they shop.
- I have a written lab test report (TDS, hardness, iron, bacteria, pH, and any health contaminants).
- I know which contaminants I actually need to remove, and which I do not.
- I have decided point-of-use, whole-house, or both.
- I have measured my peak flow and line pressure, and sized accordingly.
- I have written down the 5-year running cost, not just the sticker price.
- I have confirmed whether cartridges are standard or proprietary.
- I know who services the unit and how fast they respond.
- I have read the warranty and know exactly what it covers.
- I have asked the dealer all eight questions above.
- For any health-critical contaminant, I have confirmed the plan with a certified lab or professional.
Ten boxes. If all ten are ticked, you are buying with your eyes open, and you have quietly dodged the two most expensive mistakes: buying the wrong technology, and buying a machine that costs a fortune to keep running. Every item on that list exists because I have watched it go wrong, from an RO unit bought for water that only measured 150 TDS to a whole-house filter sized for a flat that then throttled the shower. For the full field guide to those errors, our roundup of common water filter and treatment mistakes to avoid maps each one back to a box on this checklist.
Frequently Asked Questions
What should I check before buying a water filter?
Check six things in order: your lab test results, your peak flow and line pressure, your total 5-year running cost, the maintenance and spares situation, the warranty scope, and the dealer’s answers to specific questions. The test report drives everything, never buy hardware before you know what is in your water.
What questions should I ask a water treatment dealer?
Ask which contaminants from your report it removes and to what level, the real flow rate at your pressure, the yearly cost of every consumable, whether cartridges are standard or proprietary, what the warranty covers, who services it, and how much water an RO unit wastes. Good dealers answer without deflecting to a TDS pen.
How do I size a treatment system for my home?
Size for peak demand, not average. Add up fixtures likely to run at once, allowing roughly 6-12 litres per minute each. A 3-4 person home usually peaks around 15-25 LPM and suits a 1-inch Big Blue whole-house housing. Also confirm your line pressure meets the unit’s minimum, or budget for a booster pump.
Is a TDS meter enough to decide what filter I need?
No. A TDS meter measures only total dissolved solids and tells you nothing about bacteria, iron, nitrate, arsenic or fluoride, the contaminants that actually matter for health. Treat the free “TDS demo” as a sales prop, not a test. A proper lab panel is the only reliable basis for a buying decision.
How much should I budget for filters and servicing each year?
It varies with your water, but many homes spend roughly ₹2,000, ₹6,000 a year on cartridges, membranes, UV lamps and an annual service. Muddy borewell water and high TDS push this higher by clogging filters and shortening membrane life. Always price consumables by part before you buy, not after.
So, where does that leave you?
Buying a water treatment system is not really a hardware decision, it is an information one. Get your test report, know your flow, price the running costs, and ask the eight questions, and the “confusing” purchase becomes a simple match between a spec and a machine. The checklist does the worrying so you do not have to.
When you are ready to turn these boxes into an actual buying decision, our guide to choosing the right water treatment system walks through matching each technology to your test results, so the checklist and the choice line up perfectly. Take it slow, trust your numbers, and you will only buy this once.
