Three jobs, not one gadget. Activated carbon traps molecules on its huge internal surface: chlorine, taste, disinfection by-products, longer-chain PFAS. An ion-exchange resin in the better cartridges pulls out lead. Reverse osmosis pushes water through a membrane with pores the size of a water molecule, so almost nothing else fits through 1. Carbon and resin fill up and stop working; RO strips minerals too.
What each type actually removes. Any carbon filter handles chlorine and taste. Lead needs a filter certified to NSF/ANSI 53 for lead specifically; certified ones hit 99% in real homes 2. The standard Brita isn't certified for lead; the Brita Elite, ZeroWater, and most under-sink carbon blocks are.
PFAS is where cheap filters fall apart. Under-sink dual-stage and reverse osmosis remove them near-completely; pitcher and fridge filters were all over the map, and some expired ones made the water worse than the tap 3. The EPA now caps PFOA and PFOS at 4 parts per trillion and calls zero the only safe level 4.
Why bother, if the water tastes fine. Disinfection by-products track with a 24% higher bladder-cancer rate in men, against a roughly 1-in-25 lifetime baseline over 40 years of the same water 5. A 2025 review confirmed that and added a colorectal signal, visible below the current EPA limit 6. PFAS don't leave your body; lead has no safe threshold. None of it announces itself, which is why filtering is easy to skip.
Figure out your water before you buy anything.
What you'll notice, and what you won't. Within days the water tastes like water and the chlorine smell is gone. Within weeks coffee and the kettle taste cleaner. Across decades nothing you'd notice happens, which is the point: the bladder- and colorectal-cancer odds run a little lower 6, and the PFAS your filter blocked never become part of your body. The payoff is a risk you can't feel, for the price of a cartridge.
The fine print — when to skip it, and what people get wrong
Common wrong beliefs. A standard pitcher is certified for chlorine taste only; lead and PFAS pass through. Bottled water is often filtered tap sold back, plus microplastics. Boiling kills microbes but concentrates lead and PFAS.
The RO mineral question. Reverse osmosis strips calcium and magnesium too; deficiency showed up only in people on low-mineral diets who switched to RO-only water 7. A $30 remineralisation cartridge or a normal diet closes it.
Where it fails. Expired cartridges above all: carbon fills up, does nothing, and can release PFAS it was holding 3. Also downstream lead from old fixtures, and boxes labelled "tested to NSF standards" (self-tested) versus "NSF Certified" (third-party).
- 1Cherian AG, Liu Z, McKie MJ, Almuhtaram H, Andrews RC (2023). Microplastic Removal from Drinking Water Using Point-of-Use Devices. Polymers. link
- 2Tang M, Lytle D, Achtemeier R, Tully J (2023). Reviewing performance of NSF/ANSI 53 certified water filters for lead removal. Water Research. link
- 3Herkert NJ, Merrill J, Peters C, Bollinger D, Zhang S, Hoffman K, Ferguson PL, Knappe DRU, Stapleton HM (2020). Assessing the Effectiveness of Point-of-Use Residential Drinking Water Filters for Perfluoroalkyl Substances (PFASs). Environmental Science & Technology Letters. link
- 4EPA (2024). PFAS National Primary Drinking Water Regulation. link
- 5Villanueva CM, Cantor KP, Cordier S, Jaakkola JJK, King WD, Lynch CF, Porru S, Kogevinas M (2004). Disinfection byproducts and bladder cancer: a pooled analysis. Epidemiology. link
- 6Helte E, Söderlund F, Säve-Söderbergh M, Larsson SC, Åkesson A (2025). Exposure to Drinking Water Trihalomethanes and Risk of Cancer: A Systematic Review of the Epidemiologic Evidence and Dose–Response Meta-Analysis. Environmental Health Perspectives. link
- 7Kozisek F (2005). Health Risks from Drinking Demineralised Water. link
Related in the handbook (7)
- — Only reverse osmosis reliably catches microplastics; the filter choice is how you cut that exposure at home.
- — A copper vessel is a folk water-treatment method; a real filter is the dependable alternative.
- — PFAS from non-stick coatings and industry end up in drinking water; certain filters are built to take them out.
- — The filter logic here applies to your shower head too — and chloramine needs different media than chlorine.
- — Knowing the contaminants in your supply is the input that decides which filter type you need.
- — Whether you want to keep or remove fluoride helps decide if a basic carbon filter or RO is right for you.
- — Reverse osmosis strips minerals out along with the bad stuff, so RO and remineralizing go together.
Water Filter Types
Buy once, install once. The real work is remembering to change cartridges every few months.
A jug-style filter is under $100/year; a quality under-sink system runs $300–950 up front plus $50–250/year in cartridges.
Removal performance is heavily studied and third-party certified. The bigger uncertainty is whether the individual health payoff is large or modest.
Cuts decades of low-dose exposure to disinfection by-products, lead, and PFAS — small individual risk shifts that add up across a lifetime.
Drinkable tap water shifts hydration habits within days — that's the only short-term win; the chemical-removal benefits are slow and invisible.