How to Choose a Water Filter for Your Home

Choose a water filter based on what you need to reduce, not on how many filtration stages appear on the box.

No household filter removes every contaminant. A filter that improves chlorine taste may not reduce lead. A system designed for lead may not disinfect water. A device that removes microorganisms may not remove dissolved chemicals.

Use this order:

1. Identify the water source.
2. Define the contaminant or treatment goal.
3. Decide whether treatment is needed at one tap or throughout the home.
4. Find a product certified for the specific reduction claim.
5. Check capacity, flow, installation, and maintenance costs.

Do not begin with a brand or technology. Begin with the water problem.

Decide whether you need a filter

If you use a public water system, start with the utility's annual report and any current notices.

Our guide to reading your drinking water quality report explains how to interpret detected contaminants and violations.

Remember that a system-wide report cannot describe every household faucet. Older service lines, building plumbing, fixtures, and storage systems may create household-specific concerns.

If you use a private well, follow a routine testing plan and ask the local health department about contaminants associated with local geology and land use.

Testing should come before treatment when there is a health-related concern. Our guide to testing tap water explains when a home kit may be sufficient and when a state-certified laboratory is more appropriate.

You may decide that you do not need a filter if the water meets your needs and no relevant contaminant has been identified.

A filter may still be reasonable for an aesthetic concern such as chlorine taste or odor. Keep that goal separate from a health-related reduction claim.

Define the problem in one sentence

Before comparing products, write down what the system must do.

Examples include:

• improve chlorine taste and odor
• reduce lead at the kitchen faucet
• reduce a specific PFAS compound identified in the water
• reduce nitrate in private-well water
• soften hard water to limit scale
• disinfect private-well water affected by microorganisms
• remove sediment that is clogging fixtures

“Make the water pure” is not a useful treatment goal. It does not identify the substance, concentration, treatment location, or performance needed.

If you do not know what needs to be treated, do not buy the most expensive system and assume it covers everything.

Point-of-use or whole-house treatment?

Home treatment systems are often divided into point-of-use and point-of-entry systems.

Point-of-use treatment

A point-of-use system treats water at one location or for one purpose.

Examples include:

• pitcher filters
• countertop filters
• faucet-mounted filters
• refrigerator filters
• under-sink filters
• under-sink reverse osmosis systems

Point-of-use treatment is often appropriate when the main concern is water used for drinking and cooking.

Advantages may include:

• lower purchase and installation cost
• less water treated unnecessarily
• easier verification at the treated tap
• simpler cartridge replacement

Limitations include:

• untreated water at other faucets
• limited flow or storage capacity
• multiple devices if several taps need treatment
• user dependence on timely cartridge replacement

Point-of-entry treatment

A point-of-entry system, also called a whole-house system, treats most or all water entering the home.

It may be considered when:

• exposure can occur through more than drinking and cooking
• sediment or hardness affects plumbing and appliances
• the contaminant needs to be addressed at multiple fixtures
• a well-water treatment plan requires centralized treatment

Whole-house treatment is not automatically better.

It costs more, treats a larger volume, and may require professional sizing, installation, wastewater handling, electrical service, pretreatment, and ongoing monitoring.

CDC also cautions that removing chlorine or another disinfectant from all water entering a home may allow more microbial growth in household plumbing. This does not mean whole-house carbon treatment is always inappropriate. It means the decision should account for building plumbing, maintenance, water age, and the original treatment goal.

Match the technology to the contaminant

Technology names describe how a system works. They do not guarantee that every product using that technology has the same performance.

Always verify the claim for the exact model.

This table is a starting point, not a product recommendation.

Activated carbon filters

Many pitcher, refrigerator, faucet-mounted, and under-sink filters use activated carbon.

Carbon can adsorb certain substances onto its surface. It is commonly used to improve chlorine taste and odor.

Some carbon-based products also carry certified claims for contaminants with health effects. Those claims may include lead or selected organic chemicals. Some products are certified for reduction of specific PFAS compounds.

Do not assume every carbon filter has these capabilities.

Check:

• the exact contaminant-reduction claim
• the model number
• rated capacity
• maximum flow rate
• required water conditions
• replacement interval

A carbon cartridge can reach the end of its useful capacity before it looks damaged. Taste is not a reliable indicator for contaminants that have no noticeable taste or odor.

Reverse osmosis systems

A point-of-use reverse osmosis system uses pressure to move water through a semipermeable membrane. It produces treated water and a separate reject stream.

RO can reduce many dissolved substances, but performance still depends on the model and its certified claims.

Consider RO when testing identifies a contaminant for which an appropriate certified RO reduction claim is available.

Before buying, check:

• which contaminants the exact system is certified to reduce
• treated-water production rate
• storage-tank size, if present
• reject-water ratio
• incoming pressure requirements
• pretreatment requirements
• filter and membrane replacement costs
• space and drainage needs

RO should not be the automatic choice for every household. EPA notes that conventional point-of-use RO systems can send several gallons of reject water to the drain for each gallon treated. WaterSense-labeled point-of-use RO systems must meet an efficiency criterion of no more than 2.3 gallons of reject water per gallon of treated water.

A WaterSense label addresses EPA's efficiency and performance criteria for eligible point-of-use RO systems. You must still confirm the contaminant-reduction certification needed for your water.

Ultraviolet treatment

Ultraviolet systems use UV light to inactivate microorganisms.

They do not remove dissolved chemicals such as lead, nitrate, arsenic, or PFAS.

UV performance depends on factors such as:

• UV dose
• water clarity
• flow rate
• lamp condition
• sleeve cleanliness
• system design

Sediment, color, or cloudiness can interfere with UV transmission. Pretreatment may therefore be required.

Under NSF/ANSI 55, Class A and Class B systems have different intended uses. NSF describes Class A systems as designed to inactivate or remove microorganisms from contaminated water. Class B systems are intended to reduce non-disease-causing bacteria in water already considered disinfected.

Do not treat a Class B device as a substitute for a system intended to address microbiologically unsafe water.

Water softeners

A conventional water softener primarily reduces hardness caused by calcium and magnesium.

Hardness can contribute to scale, spots, and reduced appliance efficiency. It is usually an aesthetic or operational issue rather than proof that the water is unsafe.

Softeners use ion exchange and are commonly regenerated with sodium or potassium chloride.

Do not assume a softener removes lead, nitrate, PFAS, microorganisms, or every metal. Some ion-exchange systems are designed for particular contaminants, but the exact media and verified performance claim matter.

Sediment and membrane filters

Sediment filters capture particles such as sand, rust, or silt.

They may protect downstream treatment components or improve visible clarity. They do not establish that the water is microbiologically or chemically safe.

Membrane categories such as microfiltration, ultrafiltration, and nanofiltration have different pore-size ranges and removal capabilities.

Pore size alone does not describe the entire system. Look for whether the pore size is nominal or absolute and whether the complete product has a verified reduction claim.

A nominal rating describes an average or approximate performance. An absolute rating indicates a defined maximum pore size under the test conditions. Do not treat the two labels as equivalent.

What NSF standards mean

NSF/ANSI numbers are not rankings. A larger number does not mean a better filter.

The standards address different technologies and performance categories.

Common examples include:

The standard number alone is not enough.

A product certified under NSF/ANSI 53 is not necessarily certified for every contaminant addressed by that standard. One model may carry a lead-reduction claim. Another may carry a cyst-reduction claim. The label and certification listing must identify the applicable performance claims.

The safest buying sequence is:

1. Write down the contaminant.
2. Identify the standard and claim relevant to that contaminant.
3. Record the complete product and model number.
4. Search the certifier's official database.
5. Confirm that the exact model is listed for the exact reduction claim.

NSF provides a searchable database of certified drinking-water treatment units. Other accredited certification organizations also maintain product listings.

Do not rely only on a retailer's description, marketplace badge, or phrase such as “tested to NSF standards.” “Tested to” and “certified by” are not necessarily equivalent statements.

How to check a lead-reduction claim

Do not buy a filter for lead based only on the words “carbon filter,” “multi-stage,” or “heavy metal protection.”

Verify that the exact model is certified for lead reduction under an applicable standard, commonly NSF/ANSI 53 or NSF/ANSI 58.

EPA provides a consumer tool for identifying point-of-use and pitcher filters certified to reduce lead.

Lead can vary among homes and faucets because service lines and plumbing materials differ. Our planned lead article will explain household sampling and exposure-reduction decisions in detail.

How to check a PFAS-reduction claim

Not every carbon or RO filter is certified for PFAS reduction.

Check whether the exact product is certified for the specific PFAS reduction claim. EPA provides guidance on identifying drinking-water filters certified to reduce PFAS.

Current certifications may address particular PFAS compounds and test conditions. Do not convert a claim for one group or compound into a promise to remove every PFAS substance.

Filter performance also depends on timely replacement. A cartridge that has exceeded its rated capacity may not provide the certified reduction.

Flow rate, capacity, and usable performance

A filter must work under real household conditions.

Compare:

• Flow rate: How quickly can it deliver treated water?
• Capacity: How many gallons can it treat before replacement under the rated conditions?
• Pressure: Does your plumbing meet the operating range?
• Water quality: Does the incoming water require sediment control, softening, or another pretreatment?
• Daily demand: Can it supply the amount used for drinking and cooking?
• Space: Will the unit, tank, tubing, and drain connection fit?

A high-capacity claim is meaningful only under the specified test conditions. Very turbid water, high contaminant loading, unusual chemistry, or heavy use may shorten practical service life.

Calculate the true cost

The purchase price is only one part of the cost.

Include:

• replacement cartridges
• RO membranes
• UV lamps and sleeves
• electricity
• water used for backwashing or RO reject flow
• salt or potassium chloride for softeners
• laboratory verification
• professional installation
• service calls
• safe disposal where special requirements apply

Estimate the cost over at least one year. A low-priced device with frequent proprietary cartridges may cost more than a higher-priced system with longer service intervals.

Do not extend a cartridge beyond its rated life simply to reduce cost.

Maintenance is part of treatment

A filter does not remain effective indefinitely.

Follow the manufacturer's instructions for:

• cartridge replacement
• membrane replacement
• cleaning and sanitizing housings
• UV lamp and sleeve maintenance
• softener salt and regeneration
• leak checks
• storage-tank maintenance
• periods of nonuse

CDC recommends maintaining filters and changing cartridges as directed to keep them working correctly and reduce the opportunity for microbial growth.

Keep a written record of installation and replacement dates. If treatment addresses a confirmed health-related contaminant, ask whether periodic testing is needed to verify performance.

An indicator light or calendar reminder estimates maintenance timing. It does not directly prove that every contaminant is still being reduced as claimed.

Filters during boil-water and other advisories

Do not assume a household filter overrides a drinking-water advisory.

During a boil-water advisory, CDC advises using bottled water or correctly boiled water even if the tap water has passed through a household or pitcher filter.

A boil-water advisory, do-not-drink advisory, and do-not-use advisory require different actions. Follow the current instructions from the utility or health department.

Boiling kills many disease-causing microorganisms. It does not remove lead or most chemical contaminants. In a chemical incident, boiling can be ineffective or inappropriate.

Warning signs in product marketing

Be cautious when a product:

• claims to remove “all contaminants”
• uses “NSF tested” without naming the certifier, standard, model, and claim
• lists a standard but not the certified reduction claim
• promises medical benefits unrelated to verified water treatment
• relies on testimonials instead of a certification listing
• does not provide replacement capacity or maintenance instructions
• has no accessible performance data sheet
• uses the same replacement claim for very different incoming-water conditions

A professional-looking test report is not the same as current third-party product certification.

A practical buying checklist

Before purchasing, confirm:

• My water source is public water or a private supply.
• I have identified the treatment goal or contaminant.
• I know whether I need point-of-use or whole-house treatment.
• The exact model is certified for the exact reduction claim.
• The certification is listed in the certifier's official database.
• The flow and capacity meet household needs.
• The system is compatible with the incoming water pressure and chemistry.
• Installation requirements are practical and safe.
• I know the cartridge, membrane, lamp, or media replacement schedule.
• I have calculated the ongoing cost.
• I know whether follow-up testing is needed.

Bottom line

Choose a water filter by working backward from the water problem.

Identify the contaminant or treatment goal. Decide where treatment is needed. Select a suitable technology, then verify that the exact model is certified for the specific reduction claim.

Do not treat a standard number as a rating or assume that one certification covers every contaminant. Check the official product listing, rated capacity, flow, replacement cost, and installation requirements.

The best filter is not the system with the most stages. It is the system that addresses the identified problem and can be maintained correctly over time.

References

1. Centers for Disease Control and Prevention. About Choosing Home Water Filters. Updated April 10, 2024. Accessed September 23, 2026.
2. Centers for Disease Control and Prevention. About Home Water Treatment Systems. Updated April 10, 2024. Accessed September 23, 2026.
3. NSF. NSF Standards for Water Treatment Systems. Accessed September 23, 2026.
4. NSF. Search for NSF Certified Drinking Water Treatment Units. Accessed September 23, 2026.
5. U.S. Environmental Protection Agency. Point-of-Use Reverse Osmosis Systems. Accessed September 23, 2026.
6. U.S. Environmental Protection Agency. Consumer Tool for Identifying Point-of-Use and Pitcher Filters Certified to Reduce Lead. Accessed September 23, 2026.
7. U.S. Environmental Protection Agency. Identifying Drinking Water Filters Certified to Reduce PFAS. Updated November 18, 2025. Accessed September 23, 2026.
8. Centers for Disease Control and Prevention. Drinking Water Advisories: An Overview. Updated March 4, 2024. Accessed September 23, 2026.