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What Is Filtered Water?

Written and reviewed by the BWF Team, a certified water specialist, a former municipal plant operator, a licensed plumber and a former system dealer.

Filtered water is water that has been passed through something, and that is the whole of what the phrase guarantees. It describes a process rather than a result. Two bottles both honestly labelled filtered water can have had completely different things removed from them, or nearly nothing at all.

This is not an opinion about marketing. The FDA regulation that says what bottled water may be called defines artesian, ground, mineral, purified, spring and well water, several with hard requirements. "Filtered water" appears in that regulation exactly once, in the list of terms it excludes.

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The words that carry requirements

21 CFR 165.110 is the standard of identity for bottled water. It lists the names a bottler may use and what each one obliges them to do. Some of those obligations are specific enough to fail.

Name What it requires
Mineral water Not less than 250 ppm total dissolved solids, from a protected underground source. No minerals may be added.
Purified water Produced by distillation, deionization, reverse osmosis or other suitable process, and meets the definition of purified water in the US Pharmacopeia.
Distilled water Purified water where the process used was distillation. Named for the method.
Reverse osmosis water Purified water where the process used was reverse osmosis.
Spring water Collected at the spring or through a bore hole tapping the formation feeding it, with a natural force causing it to flow to the surface.
Artesian water From a well tapping a confined aquifer where the water level stands above the top of the aquifer.
Filtered water no requirement attached Not a defined name. It appears in the regulation only in the list of ingredient terms that bottled water does not include.

Mineral water is the clearest of them. To use the name, the water must contain not less than 250 parts per million of total dissolved solids, present at the source, and the regulation adds that no minerals may be added to it. That is a number a laboratory can check, and a bottler who gets it wrong has mislabelled a food.

Purified water is nearly as tight. It has to have been produced by distillation, deionization, reverse osmosis or a comparable process and meet the US Pharmacopeia definition of purified water, which the regulation incorporates by reference. Distilled water and reverse osmosis water are the same category named for the method used.

Filtered water is not one of them

The phrase does appear in that regulation, and where it appears is the interesting part. Paragraph (a)(1) says bottled water "does not include those food ingredients that are declared in ingredient labeling as 'water,' 'carbonated water,' 'disinfected water,' 'filtered water,' 'seltzer water,' 'soda water,' 'sparkling water,' and 'tonic water.'"

So "filtered water" sits in the rulebook as an ingredient term, in a list of things the bottled water standard is not about. There is nothing behind it to check, because there is nothing it obliges anyone to do.

This is not a scandal and nobody is being deceived. Filtering water is a real and useful thing to do, and most water sold or served as filtered has genuinely been filtered. The point is narrower and more practical: the word tells you an action was taken and tells you nothing about the outcome, so it cannot be the basis for choosing anything.

What to ask instead

The useful question is not whether water was filtered but what was removed, and who checked. That has an answer, it is published, and it is specific.

Each of those certifies a list of named contaminants rather than the idea of filtration, and the list is published for every certified product. Two systems can both hold standard 58 and be certified for entirely different things, which is the comparison we make on every product page.

Filtered, purified, distilled or spring

For drinking at home the practical differences are smaller than the vocabulary suggests, and they come down to what is left in.

Is filtered water safe to drink?

Tap water from a public supply in the United States is already regulated to be safe to drink, and passing it through a filter does not change that. What a filter changes is what is in the water beyond that baseline: chlorine taste for most people, and specific contaminants for anyone whose water report or plumbing gives them a reason to care.

The one real safety consideration is maintenance. A cartridge run far past its rated capacity stops removing what it was bought to remove, and a wet filter left in place for a long time is somewhere bacteria can grow. Every manufacturer publishes an interval and a rated volume, and the interval is the part worth putting in a calendar.

Your water supplier publishes an annual report of what is actually in the supply, and it is free. That document, rather than any word on a label, is what should decide whether you need a filter and which kind.

Common questions

What is filtered water?
It is water that has been passed through something. That is the whole of what the phrase guarantees, because no standard defines it. The FDA regulation that sets out what bottled water may be called defines artesian, ground, mineral, purified, spring and well water, and mineral water has to carry at least 250 parts per million of dissolved solids while purified water has to meet a pharmacopeia definition. "Filtered water" is not among those names. It appears in the same regulation once, in the list of ingredient terms that bottled water does not include.
What is the difference between filtered and purified water?
Purified water is a defined thing and filtered water is a description of a process. To be labelled purified, water has to have been produced by distillation, deionization, reverse osmosis or a comparable process and has to meet the US Pharmacopeia definition of purified water. Filtered water has no such test to pass. In practice a good home filter and a bottle of purified water may be equally good to drink, but only one of those two words tells you anything you can check.
Is filtered water the same as tap water?
It is tap water with something removed, and which something is the question worth asking. A filter certified under NSF/ANSI 42 has been tested for chlorine, taste and odour. One certified under 53 has been tested for health contaminants such as lead and cysts. Those are very different products and both are sold as filters, so the standard and the claim list are what separate them rather than the word on the front of the box.
Is filtered water safe to drink?
In the United States, tap water from a public supply is already regulated to be safe to drink, and filtering it does not make it unsafe. What a filter changes is what is in it beyond that baseline: taste and chlorine smell for most people, and specific contaminants for anyone whose water report or plumbing gives them a reason to care. The one genuine safety consideration is maintenance, because a cartridge left in far past its rated capacity stops working and can harbour bacteria.
Is filtered water better than bottled water?
On what you can verify, filtered water from a certified system is usually the stronger position, because you can look up exactly what your filter was tested to remove and you cannot always do that for a bottle. Bottled water labelled purified, mineral or spring does carry real requirements, but bottled water labelled only "drinking water" carries very few. The running cost is not close: a certified under-sink system and its cartridges cost a fraction of the same volume in bottles.
Does filtered water still have minerals?
It depends on the filter, and this is one of the real differences between types. Carbon filtration removes chlorine and organic compounds and leaves dissolved minerals largely alone. Reverse osmosis removes dissolved solids including calcium and magnesium, which is why some RO systems add a remineralisation stage afterwards. If mineral content matters to you, that distinction decides which kind of system to buy.

Where this came from

The definitions and the quoted exclusion were read from the current text of 21 CFR 165.110 on 6 August 2026, through the eCFR, which publishes the regulation as it stands today rather than as it was printed. The wording above is the regulation's, compressed but not strengthened.

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