Water Filter Types Explained

Disclosure: Water Filter To Go is reader-supported. When you buy through links on this site we may earn a small affiliate commission at no extra cost to you.

Quick Verdict: There is no universal “best” water filter type — each technology targets a specific set of contaminants and suits different household situations. This guide explains every mainstream filter type, what it removes, what it doesn’t, and who it’s best for. For curated picks in each category, see our Best Water Filters guide.

The Main Water Filter Types at a Glance

Activated Carbon Filters

Activated carbon is the most widely used filter media in consumer water filtration. It works through adsorption — contaminants bind to the enormous surface area of porous carbon granules or a compressed carbon block. A single gram of activated carbon can have a surface area exceeding 1,000 square meters.

What Activated Carbon Removes

• Chlorine and chloramine (taste and odor) — NSF/ANSI 42
• Volatile organic compounds (VOCs) including benzene, toluene, and trihalomethanes
• Certain PFAS (per- and polyfluoroalkyl substances) on NSF 53-certified systems
• Some pesticides, herbicides, and industrial chemicals
• Lead (on NSF 53-certified systems using specific media)

What Activated Carbon Does NOT Remove

• Nitrates or nitrites
• Fluoride
• Heavy metals not covered by the specific certification (arsenic, mercury, unless tested for)
• Dissolved solids (TDS), hardness minerals, or salts
• Bacteria and viruses (carbon is not a disinfectant)

Formats: Granular vs. Block Carbon

Granular activated carbon (GAC) pours more freely and is used in many pitcher filters and whole-house pre-treatment stages. Carbon block filters pack finely ground carbon into a solid matrix, offering a smaller pore size, better contaminant contact time, and more consistent performance — the preferred choice for under-sink and faucet-mount systems targeting health-related contaminants. Carbon block filters with NSF 53 certification are the standard for lead and VOC reduction.

Pitchers

The most accessible entry point into water filtration. Brita, PUR, and ZeroWater are the dominant brands. Brita Standard is NSF 42 only (aesthetics); Brita Elite and PUR PLUS carry both NSF 42 and 53, covering lead and some VOCs. ZeroWater uses a five-stage ion exchange + carbon system that reduces TDS to near zero — its specialty — but filters wear out faster in high-TDS water. Pitcher filters typically need replacement every 40 gallons or approximately two months.

[Check Price on Amazon]

Faucet-Mount Filters

Attach directly to the sink faucet. PUR PLUS FM-3700 is the reference model — NSF 42 and 53 certified, covers lead and 70+ contaminants. Convenient and low cost, but slower flow than unfiltered water, and incompatible with pull-out faucet styles. Cartridges typically last 100 gallons (approximately 3 months).

Reverse Osmosis (RO) Systems

RO forces water under pressure through a semi-permeable membrane with pores small enough (around 0.0001 microns) to block dissolved salts, heavy metals, and most molecular-size contaminants. It is the broadest-spectrum home filter technology available. Certified under NSF/ANSI 58.

What RO Removes

• Total dissolved solids (TDS) — typically 90–99% reduction
• Lead, arsenic, chromium, barium, radium
• Nitrates and nitrites
• Fluoride
• Most PFAS compounds
• Bacteria, viruses, and cysts (the membrane itself is an effective physical barrier)

RO Trade-offs

• Waste water: Traditional RO systems produce 3–4 gallons of drain water per gallon of filtered water. Modern “high-efficiency” or “tankless” RO systems have improved this ratio to 1:1 or better.
• Mineral removal: RO also removes beneficial minerals (calcium, magnesium). Some premium systems add a remineralization post-filter stage. The health significance of mineral-stripped water is debated — most minerals come from food, not water.
• Flow rate: RO systems use a storage tank (typically 2–4 gallons) because the membrane produces filtered water slowly. Demand outpaces the membrane for large families.

Under-Sink RO

The most popular format. Installed under the kitchen sink with a dedicated filtered-water faucet. Standard systems have 3–5 stages: sediment pre-filter, carbon pre-filter, RO membrane, carbon post-filter, and optionally a remineralization stage. Install time for a competent DIYer is 60–90 minutes.

Countertop RO

Requires no plumbing — connects to the sink faucet via a divert valve or operates completely standalone (tank-based). The AquaTru Carafe is the leading countertop RO model, with IAPMO certifications covering 83 contaminants. Ideal for renters or anyone who doesn’t want to drill holes under the sink.

[Check Price on Amazon]

Ceramic and Hollow Fiber Filters

Ceramic filters use a porous clay material (typically diatomaceous earth) to physically block particles, bacteria, and cysts. Hollow fiber membranes work similarly, using a bundle of hair-thin tubes with pores as small as 0.1 microns to block biological contaminants.

What Ceramic and Hollow Fiber Remove

• Bacteria (E. coli, Salmonella, Legionella) — up to 99.9999%
• Protozoan cysts: Cryptosporidium and Giardia
• Sediment and turbidity

What They Don’t Remove

• Viruses (pore size too large — requires UV or RO for virus removal)
• Chemical contaminants (chlorine, VOCs, heavy metals) — usually paired with a carbon stage in multi-stage systems
• Dissolved solids or hardness minerals

Ceramic filters are common in gravity-fed countertop systems (Berkey-style, though Berkey’s certification claims have been disputed) and as a pre-filter stage in multi-stage under-sink units. Hollow fiber membranes appear in backpacking filters (Sawyer Squeeze) and some under-sink systems.

UV Purification Systems

Ultraviolet (UV) systems expose water to germicidal UV-C light (wavelength around 254 nm), disrupting the DNA of microorganisms and rendering them unable to reproduce. UV is effective against bacteria, viruses, and protozoa — including pathogens that chlorine-resistant (Cryptosporidium, in high doses, can survive low-level chlorination; UV kills it reliably).

Key Limitations

• UV does not remove chemical contaminants of any kind — it is a disinfection-only technology.
• Turbid (cloudy) water blocks UV light — the water must be pre-filtered to clear turbidity before reaching the UV lamp.
• UV systems require power (typically 10–40 watts) and lamp replacement annually.

UV is most valuable for well water users who face bacterial contamination risk, or as a final stage in a whole-house system after carbon and sediment pre-filtration.

Ion Exchange and Water Softeners

Ion exchange resins swap “hard” calcium and magnesium ions for sodium or potassium ions, eliminating scale buildup in pipes and appliances. Some resins also remove heavy metals (lead, cadmium, barium).

Traditional salt-based softeners add sodium to the water — not suitable as the sole drinking water treatment for people on sodium-restricted diets. Salt-free “descalers” (template-assisted crystallization or TAC) condition minerals to resist scale without adding sodium, but do not technically “soften” water in the classical sense. For drinking water specifically, a carbon or RO post-filter after a softener is the standard recommendation.

Whole-House (Point-of-Entry) Filtration Systems

Whole-house systems install where the main water line enters the home, filtering every tap — showers, sinks, appliances. Typical configurations:

• Stage 1: Sediment pre-filter (5–20 micron) — removes particles that foul downstream media
• Stage 2: Activated carbon (GAC or block) — chlorine, chloramine, VOCs, taste/odor
• Stage 3: Optional salt-free conditioner or KDF media for hardness and heavy metals
• Stage 4 (optional): UV disinfection — bacteria and viruses for well water

Whole-house systems are the right choice when contamination affects all household water use, when well water has bacterial or sediment issues, or when the home has older lead pipes. They do not replace a point-of-use RO system if you need the broadest chemical contaminant removal for drinking water.

Gravity Countertop Filters

Gravity filters (large countertop canisters that drip water through ceramic and carbon stages) require no plumbing or power. Popular among preparedness-minded households and those wanting filtered water without installation. Performance varies widely by brand and certification — look for NSF 42 and 53 certification on the specific model.

Which Filter Type Is Right for You?

For a deeper buying process including budget tiers and step-by-step decision making, see our Best Water Filters guide. If you’re installing your first under-sink system, read our step-by-step How to Install an Under-Sink Water Filter.

Frequently Asked Questions

What is the difference between NSF 42 and NSF 53?

NSF/ANSI 42 covers aesthetic effects — chlorine, taste, odor, and particulate. NSF/ANSI 53 covers health effects, including lead, arsenic, mercury, Cryptosporidium, Giardia, VOCs, and certain PFAS. A filter certified to both standards addresses both appearance and safety concerns. Always check the certification applies to the specific contaminants you need removed, not just the standard number.

Does reverse osmosis remove fluoride?

Yes. NSF/ANSI 58-certified reverse osmosis systems are tested and certified to reduce fluoride. Carbon block filters under NSF 42 or 53 do not remove fluoride on their own.

Can I combine filter types?

Yes, and many effective systems do exactly this. Multi-stage under-sink systems typically pair a carbon pre-filter with a hollow fiber or RO membrane. Whole-house systems combine sediment, carbon, and optionally UV. Adding a UV stage to a carbon under-sink system addresses bacteria without the cost of RO.

Are gravity filters as effective as under-sink filters?

It depends entirely on the specific model and its certifications. Some gravity systems carry NSF 42 and 53 certifications and perform well for their certified contaminants. Others have limited or disputed certification. Check the model’s specific NSF certification scope before purchasing, rather than relying on brand reputation alone.