What Water Filters Actually Remove (And Which Ones Don't)

Walk into any hardware store and you'll find an overwhelming wall of water filters — pitchers, under-sink units, countertop systems, whole-house filters, reverse osmosis setups. The marketing on all of them promises clean, pure, safe water. Almost none of it tells you what each system actually removes.

This matters because different filtration technologies target fundamentally different contaminants. A pitcher filter that excels at improving taste and removing chlorine may do nothing for lead. A system certified for lead removal may leave PFAS completely untouched. Buying the wrong filter for your actual contaminant profile is not just a wasted investment — it's a false sense of security.

The starting point is knowing what's in your water. Your utility's annual Consumer Confidence Report lists what's been detected. The EWG Tap Water Database cross-references that data against health guidelines. PollutionProfile's Water Quality feature connects your address to your water system's testing history. Once you know what you're dealing with, the filter selection becomes much more straightforward.

The four main categories of concern are: particles and sediment, heavy metals (especially lead), organic chemicals (VOCs, PFAS, disinfection byproducts), and biological contaminants (bacteria, cysts). No single filtration technology addresses all four equally well — which is why understanding the landscape matters.

Pitcher filters (e.g., Brita, Pur, ZeroWater) Best for: chlorine, chloramines, some VOCs, taste and odour improvement Not effective for: lead (standard models), PFAS, nitrates, bacteria Notes: Brita's Standard filter is not certified for lead. Their Longlast+ filter is NSF/ANSI 53 certified for lead reduction. ZeroWater uses ion exchange and removes a broader range including some heavy metals, but filter life is short. Convenient but lowest overall performance tier.

Under-sink activated carbon filters Best for: chlorine, chloramines, VOCs, some PFAS, taste, some pesticides Not effective for: nitrates, heavy metals (unless specifically certified), bacteria Notes: Carbon block filters perform better than granular activated carbon for PFAS. Look for NSF/ANSI 53 or 58 certification for specific contaminant claims.

Reverse osmosis (RO) systems Best for: PFAS, lead, arsenic, nitrates, heavy metals, DBPs, fluoride, most dissolved solids Not effective for: some VOCs (carbon post-filter addresses this), chlorine-resistant cysts (though rare in treated water) Notes: The most comprehensive technology for dissolved contaminants. Wastes 3–4 gallons of water per gallon filtered. Under-sink RO with carbon post-filter is the gold standard for households with complex contamination concerns.

Whole-house filters Best for: sediment, chlorine, some VOCs throughout all household water Not effective for: PFAS, lead, nitrates at typical whole-house filter specs Notes: Useful for improving general water quality and protecting appliances, but not a substitute for point-of-use filtration for drinking water if specific contaminants are a concern.

NSF International is the independent, not-for-profit organisation that certifies water treatment products against agreed performance standards. When a filter claims NSF certification, it means an independent laboratory has verified that it removes what it says it removes, at the concentrations claimed, under the test conditions specified.

The key standards: • NSF/ANSI 42: Aesthetic effects — chlorine, taste, odour, sediment. The minimum bar. Almost all filters meet this. • NSF/ANSI 53: Health effects — lead, cysts, VOCs, some pesticides. A significantly higher standard. Look for this if lead or VOCs are concerns. • NSF/ANSI 58: Reverse osmosis systems — covering the full range of contaminants RO addresses, including PFAS, arsenic, and nitrates. • NSF/ANSI 401: Emerging contaminants — pharmaceuticals, certain PFAS compounds, pesticides not covered under 53.

What certification means in practice A filter bearing the NSF/ANSI 53 mark for lead reduction has been tested to remove lead at a specific influent concentration (typically 150 ppb, well above normal tap water levels) to below 10 ppb. That's not the same as saying it will perform identically in your home — filter life, water chemistry, and flow rate all affect real-world performance.

What to watch for Some products display an NSF logo but are only certified under Standard 42 — the aesthetic standard. Read the fine print. "NSF certified" without specifying which standard means very little for health-relevant contaminant removal.

A filter you've forgotten to maintain can be worse than no filter at all.

The exhaustion problem Carbon filters work by adsorption — contaminants stick to the surface of the carbon. Once that surface is saturated, the filter stops adsorbing new contaminants. More concerning: bacteria can grow in an exhausted carbon filter, turning a protective device into a contamination source. RO membranes accumulate sediment and lose efficiency over time.

Replacement schedules by filter type: • Pitcher filter cartridges: every 2–3 months depending on use and water quality • Under-sink carbon filters: every 6–12 months • RO membranes: every 2–3 years; pre- and post-filters every 6–12 months • Whole-house sediment filters: every 3–6 months

Use your filter's change indicator, but verify it Most modern filters include a usage indicator. These are generally reliable for typical water quality but may not account for unusually high contaminant loads — during a water quality event, a filter may exhaust faster than the indicator suggests.

Water quality testing after installation If you've installed a filter to address a specific contaminant — particularly lead or PFAS — it's worth doing a before-and-after water test to confirm the system is performing as expected. Certified labs can test for specific contaminants for $20–100 depending on the panel.