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The short answer
How to choose a water filter comes down to one rule: buy for what’s in your water, then check that the filter is certified for it. Start with your utility’s annual water quality report or a test from a state-certified lab. List the contaminants you want to reduce. Then pick a format that fits your home, and confirm in a certifier’s directory (NSF International, IAPMO R&T, or WQA) that the exact model is certified for each one. Last, compare running costs, not just the box price.
Step 1: Find out what’s in your water
- City water: your utility must deliver its Consumer Confidence Report each year by July 1. From 2027, systems serving over 10,000 people send it twice a year.
- Lead: it usually comes from pipes and fixtures between the main and your tap, so the utility report may not show what reaches your glass. Homes built before 1986 are more likely to have lead pipes. Test at the tap.
- Private wells: they aren’t regulated by the federal government. The EPA advises testing every year for total coliform bacteria, nitrates, total dissolved solids, and pH.
- Use a certified lab. Penn State Extension advises a state-certified water testing laboratory, and confirming any salesperson’s free in-home test with an independent lab.
Step 2: List the contaminants you want to reduce
Sort your results into two groups. Health concerns, such as lead, arsenic, nitrate, PFAS, and bacteria, come first. Taste, smell, and scale problems, such as chlorine, sulfur, iron, and hardness, come second. Our guides cover the common ones: lead, PFAS, fluoride, chlorine, microplastics, and hard water.
Step 3: Match each contaminant to a technology
| Technology | What it can reduce | What it doesn’t do |
|---|---|---|
| Activated carbon | Chlorine, taste and odor, and, when certified, lead, VOCs, and PFAS | Most carbon filters aren’t certified for fluoride, arsenic, or nitrate |
| Reverse osmosis | Dissolved solids, plus certified claims such as lead, fluoride, arsenic, and nitrate (NSF) | Wastes water; removes minerals; slower |
| Activated alumina | Arsenic, fluoride, selenium, sulfate, and uranium (Minnesota Department of Health) | Narrow focus; usually part of a larger system |
| Ion exchange softener | Calcium and magnesium (hardness) (MDH) | Not a drinking water filter; adds sodium or potassium |
| UV | Kills bacteria, viruses, and other pathogens (MDH) | Removes no chemicals; needs clear water |
| Distillation | Minerals and many dissolved contaminants (MDH) | Slow, uses power; some VOCs carry over |
Step 4: Choose a format for your home
Pitcher or dispenser
Cheapest and no install. Slow, small capacity, and frequent filter changes. See the best pitchers.
Countertop
No plumbing, including countertop RO. Needs counter space and sometimes an outlet. See countertop picks.
Under-sink
Out of sight with a dedicated faucet; carbon or RO. Needs a cabinet and usually a drill. See under-sink picks.
Whole-house
Treats every tap, mostly for chlorine, sediment, or well problems. Rarely certified for drinking water contaminants. See whole-house vs point of use.
Step 5: Check the certification, model by model
A certifier tests the model to an NSF/ANSI standard, inspects the factory, and retests over time (NSF International). The EPA names five accredited certifiers: NSF International, IAPMO R&T, WQA, UL Solutions, and CSA Group (EPA). Certification covers only the contaminants named on the listing, so search the exact model and read its claims.
| Standard | What it covers |
|---|---|
| NSF/ANSI 42 | Taste and odor: chlorine, chloramine, particulates |
| NSF/ANSI 53 | Health contaminants: lead, cysts, VOCs, PFOA/PFOS, Total PFAS |
| NSF/ANSI 58 | Reverse osmosis: TDS required; lead, fluoride, arsenic, nitrate optional |
| NSF/ANSI 401 | Up to 15 emerging compounds; microplastics claims are listed here |
| NSF/ANSI 44 / 55 / 62 | Softeners / UV / distillation |
“Tested to NSF/ANSI 53” isn’t the same as certified: there’s no listing, factory inspection, or retesting. For lead, the EPA says look for a claim to reduce it to 5 ppb or less. More in our guide to NSF certification.
Step 6: Compare the running cost
- Cost per gallon: divide the replacement filter price by its rated gallons. A cheap pitcher with a 40-gallon filter can cost more per year than a pricier system.
- RO wastewater: a typical under-sink RO unit sends five gallons or more to the drain for every gallon it makes. WaterSense-labeled units send 2.3 gallons or less.
- Maintenance: Penn State notes that all water treatment equipment requires routine maintenance. Minnesota warns that unmaintained units can make water quality worse. See how often to change a filter.
Which filter fits which situation?
Each pick below is certified for the claims shown. The full comparison is in the best drinking water filters.
| # | Filter | Score | Certified by | Lead | PFAS | Fluoride | Running cost | Price |
|---|---|---|---|---|---|---|---|---|
| 01 | AquaTru CarafeMost certified claims, no plumbingCountertop RO | 4.6 | IAPMO R&T | Certified | Certified | Certified | $0.33/gal | See priceon Amazon › |
| 02 | Aquasana Claryum Max FlowUnder the sink, no wastewaterUnder-sink carbon | 4.3 | WQA | Certified | Certified | No | $0.11/gal | $449.99on Amazon › |
| 03 | Waterdrop G3P800Under-sink ROUnder-sink RO | 4.3 | IAPMO R&T | Certified | Certified | Certified | About $160/yr | $759.00on Amazon › |
| 04 | Culligan ZeroWaterPitcher with fluoride and Total PFASPitcher | 4.2 | IAPMO R&T | Certified | Certified | Certified | $0.68 to $0.93/gal | See priceat Culligan › |
| 05 | Brita EliteCheapest certified for leadPitcher | 4.1 | IAPMO, WQA, NSF | Certified | Claim | No | $0.14/gal | $47.99on Amazon › |
Certified: Certified by an independent body (named in each pick). Lab test: Tested by a named independent lab, not certified. Claim: The maker's claim, not certified. No: No claim. PFAS means PFOA/PFOS, or Total PFAS where the pick says so.
Common questions
How do I know what’s in my water?
On city water, read your utility’s Consumer Confidence Report, due each year by July 1 (EPA). For lead from your own pipes, or for a private well, test with a state-certified lab (Penn State Extension).
What certification should a water filter have?
A certification from NSF International, IAPMO R&T, WQA, UL Solutions, or CSA Group for the specific contaminant you care about: NSF/ANSI 53 for lead, 58 for reverse osmosis, 42 for chlorine taste and odor.
Do I need reverse osmosis, or is carbon enough?
Carbon filters can be certified for chlorine, lead, VOCs, and PFAS. You need RO, or another specialized method, for fluoride, arsenic, nitrate, or high dissolved solids (NSF).
How do I check whether a filter is really certified?
Search the exact model in the certifier’s directory (info.nsf.org, pld.iapmo.org, or find.wqa.org) and read the claims listed for that model, not the brand.
Should I test again after installing a filter?
Yes. The Minnesota Department of Health advises testing the treated water to make sure the treatment is working.
Sources
Prices as of October 19, 2026. Product prices and availability are accurate as of the date/time indicated and are subject to change. As an Amazon Associate we earn from qualifying purchases.