A filter is useful when it addresses a defined problem. Better-tasting water, reduced lead, and protection from particular germs are different goals. The number of stages, a clear glass of water, or a familiar brand cannot tell you which of those goals a product meets.
Updated September 7, 2026. U.S. household guidance; equipment instructions and local requirements vary.
Start with the water, not the appliance
Write down the reason you are considering treatment: a taste complaint, a laboratory result, a plumbing concern, or advice from your water supplier. If there is no harmful contamination, treatment may be optional. A shopping comparison becomes much easier when it begins with a named concern rather than “everything that might be in water.”
For community-supplied water, obtain the supplier’s current Consumer Confidence Report and read its reporting period, detected contaminants, and notices. The EPA’s consumer report guidance explains this annual report. It describes the system’s water; ask the utility or health department whether your particular plumbing concern calls for a tap sample.
Private wells need their own testing plan. CDC recommends annual testing for total coliform bacteria, nitrates, total dissolved solids, and pH, using a state-certified laboratory. Local health officials can identify additional concerns and help interpret results. Keep the actual report, units, sampling date, and sampling instructions with your filter research.
Read the exact certified claim
On a narrow screen, scroll this table sideways. Keyboard users can focus the table region and use the arrow keys.
| Mark or standard | What it addresses | What to verify |
|---|---|---|
| NSF/ANSI 42 | Aesthetic effects, such as a specified taste or odor reduction. | The particular claim; this alone is not proof of lead reduction. |
| NSF/ANSI 53 | Specific contaminants with health effects. | The named contaminant, exact model, and cartridge combination. |
| NSF/ANSI 58 | Reverse-osmosis drinking-water treatment systems. | Which reduction claims apply to this system. |
| NSF/ANSI 401 | Specified emerging or incidental contaminants. | Which compounds appear in the certified listing. |
NSF explains the standards and their limits: a standard number does not mean a system reduces every possible contaminant. Certification to a higher number is not a higher overall rating.
Search the certifier’s listing for the complete model identifier, then compare the performance data sheet with the replacement cartridge sold locally. For a lead concern, the NSF lead-reduction listings provide a starting point. A claim for one cartridge should not be transferred to another that merely fits the same housing. Save the listing link and the date you checked it.
Choose a treatment format that fits
Point-of-use treatment serves a particular drinking-water outlet or batch. Whole-home treatment handles water as it enters the property. A kitchen drinking-water problem does not automatically require treating every shower and hose bib. CDC’s overview of treatment systems distinguishes filtration, reverse osmosis, ultraviolet treatment, distillation, and softening; these processes are not interchangeable.
Pitcher, dispenser, or faucet filter
Compare the certified claim first, then capacity, refill effort, faucet compatibility, and cartridge availability. A large household may find a small pitcher inconvenient even when its treatment claim is suitable.
Under-sink filtration
Check cabinet space, service access, the required faucet arrangement, pressure limits, and installation costs. Include replacement housings or proprietary parts in the decision.
Reverse osmosis
Check certified contaminant claims, treated-water output, storage or power needs, and reject-water plumbing. Compare water efficiency as well as purchase price.
Whole-home or specialized treatment
Ask a qualified water-treatment professional to connect the test results to a system design, service plan, and verification method. A softener’s hardness treatment is not a general drinking-water safety guarantee.
RO produces both treated and reject water. EPA’s WaterSense guidance explains its efficiency label and cautions that RO is not necessary for every application. Confirm the actual reduction claims even when a product carries an efficiency label.
Plan cartridge life and total cost
Use the manufacturer’s time and volume replacement limits, and follow whichever applicable limit is reached first. Include initial preparation, flushing, cleaning, and any restart instructions after non-use. A reminder light is not a laboratory test proving the water is safe. CDC’s filter-selection guidance emphasizes matching treatment and maintaining the system.
The downloadable filter selection and service record holds the water concern, exact model and cartridge, certified claim, replacement limits, and cost assumptions. Recheck the record when changing cartridges or when water conditions change.