Marketing copy tends to say “removes contaminants” without saying which. Different filter technologies handle completely different problems, and buying the wrong one is the most common mistake in this category.
Activated carbon
The most common household filter — used in pitchers, faucet mounts, fridge filters and most under-sink systems. Carbon adsorbs chlorine, chlorine by-products, many volatile organic compounds, and the tastes and odours that come with them. Higher-grade carbon block filters, when certified to NSF/ANSI 53, also reduce lead and cysts.
What it does not do: remove dissolved minerals, nitrates, sodium or fluoride, and it does not disinfect.
Reverse osmosis
Forces water through a membrane fine enough to block dissolved solids. This is the broadest household filtration available — nitrates, arsenic, fluoride, sodium and total dissolved solids all come down substantially.
The trade-offs: it sends some water to drain, strips beneficial minerals along with everything else, and produces water slowly.
Sediment filters
Mechanical strainers rated in microns. They catch sand, rust and grit. They do nothing chemically, but they protect finer filters downstream from clogging — which is why they sit first in almost every multi-stage system.
UV disinfection
Ultraviolet light inactivates bacteria, viruses and protozoa. It is the standard answer for private wells with a bacterial problem. It removes nothing physically or chemically — the water leaves with exactly the same mineral content — and it only works on clear water, so it always sits after filtration.
Water softeners
Not filters at all, strictly speaking. Ion exchange swaps calcium and magnesium for sodium, which stops scale. It does not improve taste, remove chlorine or address contaminants.
Matching the tool to the problem
Read your municipal water report, or test your well. Then buy for what the results show. A pitcher will not fix hardness, a softener will not remove lead, and reverse osmosis is overkill for water that simply tastes of chlorine.
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