Independent No paid links, anywhere
Buy the filter your water test calls for, not the one on the box
Filter buying usually runs backwards: pick a product, then find a reason. That is how households end up with a carbon filter bought for nitrate. WaterSpec Lab runs it forwards — from your measured number to the models certified for it.
Start here
Which of these is you?
The supply you are on decides which rules protect you, what has already been measured, and who is responsible for the rest.
I am on city water
Your utility treats to a federal limit and sends you a report proving it. Three gaps it cannot close are yours.
Start hereI am on a private well
No federal limit applies to you and nobody tests it for you. The whole sequence starts with a test you commission.
Start hereI already have test results
Then the question is which technology addresses your number, which NSF claim names it, and which models hold that claim.
Start hereThe method
How do you choose a water filter without guessing?
Work in one direction only. Reverse it and you are buying a badge on a box with no way to check what it covers. Every step below is free, and every step is verifiable by you.
- 1
The number
A figure from your annual report, or from a test of your own tap. Nothing downstream can be decided without one.
- 2
The technology
EPA names Best Available Technologies per contaminant. That decides which family of product can work at all.
- 3
The claim
NSF records certification per claim and per model, not per standard. Search the claim by name.
- 4
The model
Confirm the specific model appears under that claim. Brands are not certified; models are.
What you get
What does WaterSpec Lab give you that a review site does not?
Three things, none of which is an opinion about a product. All of it is free to read, and none of it is paid for by a manufacturer.
615
Certified models, counted
Distinct models holding an NSF lead reduction claim, parsed from NSF's own listing and checked against the total NSF itself reports. Cyst returns 1,104. Nitrate returns 84, and every one is the same product form.
Every roster, claim by claim33
Regulated, with nothing certified
Crossing EPA's 94 regulated entries against NSF's claim list leaves this many with no certified reduction claim of that name. Nobody else publishes the crosswalk, and it is the answer to a question products cannot answer.
Which ones, and why459
Figures that trace to a source
Every number on this site is in a register with the passage it came from quoted verbatim, the date it was captured, and what the source does not cover. The build refuses to publish a figure that is not.
How the register worksFair questions
The objections worth answering
Is this just another affiliate site?
Not today, and the switch is in public. Four applications are pending and none is approved, so there is not one paid link on this site. When that changes, the disclosure and the sponsored link attributes turn on from the same file that records the approval, and the build asserts it on the deployed pages.
The disclosure, and the current statusWhy trust numbers on a website?
Because you do not have to. Each figure carries its source, the quoted passage, and a capture date, so you can check it against the original in about a minute. A script re-runs every recorded NSF query against the live listing and flags any count that has moved.
Check a claim yourselfI just want to be told which one to buy.
That is the honest limit here. Nobody who has not seen your test results can name a model for you, and the ones who do it anyway are guessing or selling. What this site can do is narrow it to the claim your number needs, and the models that hold it.
Which claims exist, and how populated each is17 pages
City water and how it is regulated
I am on municipal water. What is already handled, and what do I treat myself?
City water treatment — what your utility does, and what it leaves to you
Your utility treats to enforceable federal limits and sends you an annual report proving it. What it cannot reach is your own plumbing, the band between a health goal and a legal limit, and anything not yet monitored. Those three are what a household filter is for.
Boil water notices — what boiling fixes, and the two things it makes worse
I have a boil water notice. What do I actually do, and does boiling handle everything?
Coliform bacteria on city water — an indicator, not a pathogen
My water system reported coliform bacteria — what does that mean and is it a violation?
Cross-connections and backflow — how contamination gets into a main
How does contamination get into the water main, and is backflow something I can fix?
Cryptosporidium and Giardia — why EPA requires removal, not disinfection
Does my water filter remove Cryptosporidium and Giardia, and does city water already handle them?
Ground water systems — the rule that does not require disinfection
Does my water get disinfected if my system uses ground water, and what rule applies?
Home plumbing materials — what the pipe after the meter adds
What are my pipes made of, and can my own plumbing put something into the water?
How to read your water quality report — the four columns that matter
My water utility sent me an annual report. What do the numbers actually mean?
Legionella — regulated with no limit, and no filter certified against it
Is Legionella in tap water regulated, and can a filter do anything about it?
Main breaks and new pipe — what a repair does to your water
There was a water main break or pipe work near me — what does that do to my water?
Nitrification — what happens to chloramine between the plant and your tap
My water is chloraminated and something changed. What is nitrification and does it reach me?
Public notice tiers — how fast a water violation has to reach you
I got a notice from my water utility. How serious is it, and how can I tell?
Stagnant water — what sitting in the pipes does, and what flushing actually fixes
The house was empty for a while. Is the water still fine, and what should I actually do?
Testing city water — what your utility already measured, and what it did not
Should I test my city water, and what should I test for?
Turbidity — the line on your report that is really a pathogen check
My water report lists turbidity. What is it and should the number worry me?
Unregulated contaminants — what EPA watches, and what your utility tested anyway
What about contaminants with no drinking water limit — is anyone measuring them?
Water age — why the same supply differs from street to street
Why does my water taste or look different from my neighbour's, or different in summer?
19 pages
What is actually in it
Which contaminants actually matter in my water, and how do I tell them apart?
What is in city water — the regulated, the advisory, and the unmeasured
Contaminants fall into three groups, and the group decides what you can do. Some carry an enforceable limit your utility must meet. Some carry only an advisory figure that binds nobody. Some are measured by nobody at all. Only the first group gives you a number to act on.
Algal blooms and cyanotoxins — advisory numbers, no limit, one certified claim
My water system had an algal bloom — is there a limit for cyanotoxins and can I filter them?
Asbestos in drinking water — the pipes are the source, and the limit counts fibre length
Is asbestos in tap water regulated, where does it come from, and can it be filtered?
Chlorine vs chloramine — why the jug-on-the-counter trick stops working
My city water tastes of chlorine — what removes it, and does it matter which one they use?
Chromium-6 — one limit for two forms, and the claim that names only one
Is there a chromium-6 limit in drinking water, and which filters are certified for it?
Copper and blue-green staining — the visible half of the Lead and Copper Rule
My sink has blue-green stains and a metallic taste. What is it and does it matter?
Disinfection byproducts — TTHM, HAA5, and the number that is an average
My water report lists TTHM and HAA5. What are they, and do I need to treat for them?
Fluoride in drinking water — the two limits, and which one your report is measured against
How much fluoride is in my water, is it too much, and what removes it?
Lead in drinking water — the new action level, and the two things you are owed
Is there lead in my water, and what do I do about it?
Lead in school drinking water — "Filter First", and which claim carries the lead
Is lead in school and childcare drinking water regulated, and what does a Filter First certification mean?
Manganese — three numbers, none enforceable, and nothing to search for
My water has black or brown staining. Is manganese harmful and what can I do about it?
Microplastics — one certification exists, and 806 models hold it
Do water filters remove microplastics, and which ones are actually certified?
Nitrate on city water — the one chemical limit EPA treats as an emergency
What does a nitrate result on my city water report mean, and what removes it?
PFAS in drinking water — the limits, and what a certified filter does not prove
Is PFAS in my water, and which filter actually gets it below EPA's limit?
Pharmaceuticals in tap water — unregulated, and certified against anyway
Are pharmaceuticals in drinking water regulated, and can any filter be certified to reduce them?
Radium and uranium in city water — four standards, one certified filter claim
What are the radionuclide limits on my water report, and can a filter reduce them?
Radon in water — the rule proposed in 1999 and never finalised
Is radon in my tap water regulated, and should I filter it?
TDS meters — what the number in the shop demo actually measures
My TDS reading is high. Does that mean my water is unsafe?
Why your water tastes, smells or looks wrong — the 15 standards nobody has to meet
My water tastes, smells or looks odd — what causes it and does it matter?
16 pages
Choosing treatment
How do I actually choose a water filter without guessing?
Choosing water treatment — from a number on your report to a listed model
Work in one direction only: a measured figure, then the technology that addresses it, then the NSF claim by name, then a model holding that claim. Reverse the order and you buy a badge. Most of what goes wrong is choosing a product before knowing which claim you need.
33 regulated contaminants with no certified filter claim
Is there a certified filter for every contaminant EPA regulates?
Distillation — the standard with no searchable claims
Should I buy a water distiller, and why can I not find one certified for my contaminant?
Does your filter remove it? What NSF certifies, claim by claim
Does my water filter remove fluoride, chloramine, PFAS or nitrate — and how do I find out?
Filter maintenance — the running cost, and the failure you cannot see
When should I change my water filter, and what happens if I do not?
How to check NSF certification — and the footnote that withdraws the claim
How do I check whether a water filter is really NSF certified, and what does the listing actually say?
How to choose a water treatment system — seven questions that decide it
How do I decide which water treatment system I need?
Is softened water bad for you? The sodium question, worked
Does a water softener add enough sodium to matter, and what do I do about it?
Micron ratings — why "1 micron" on the box can mean two different things
What micron rating do I need, and what does the number on the filter actually mean?
NSF/ANSI 42 vs 53 vs 44 vs 58 vs 401 — what each certification covers
What does each NSF/ANSI water treatment standard certify, and what does it not?
Pitcher, faucet mount, under-sink or fridge filter — what each form can be certified for
Which type of water filter should I buy — pitcher, faucet mount, under-sink or refrigerator?
Point-of-use or whole-house? The exposure route decides it
Do I need a whole-house filter or just one at the kitchen tap?
Reverse osmosis on city water — what NSF/ANSI 58 actually certifies
Do I need reverse osmosis on city water, and what does certification cover?
Salt-free vs salt-based water softeners — which one your test result calls for
Do salt-free water softeners actually soften water, and which should I buy?
What EPA says removes what — Best Available Technology, and what you can buy
Which treatment technology actually removes each contaminant, according to EPA?
What water treatment system do you need? The sizing method, shown
Given my water test numbers, which system do I need and what size?
13 pages
What is certified, counted
How many filters are actually certified for my contaminant, and which ones?
The certified rosters — every claim counted, model by model
Each roster on this site is one NSF claim search, parsed and counted, with the extracted row count checked against NSF's own reported total. The fields differ enormously: 615 models hold a lead claim, 84 hold nitrate, 28 hold Filter First. The count itself is usually the finding.
Bottled water vs tap — two regulators, and the report you stop receiving
Is bottled water actually safer than tap water, and is it worth the cost?
Filters certified for arsenic — every claim is conditional, and on two things
Which filters are certified to remove arsenic, and what do I need to know before buying one?
Filters certified for chloramine — the 137, and the categories with none
My utility uses chloramine. Which filters are actually certified to reduce it?
Filters certified for cysts — 1,104 models, and twelve you can carry
Which water filters are certified to remove Cryptosporidium and Giardia?
Filters certified for fluoride — 127 models, and all of them the same format
Which water filters are actually certified to reduce fluoride?
Filters certified for lead — the 615, and the category with none
Which water filters are actually certified to reduce lead, and what format should I buy?
Filters certified for nitrate — 84 models, and the claim that carries the rest
Which water filters are certified to reduce nitrate, and what do I need to know before buying?
Filters certified for PFAS — every model NSF lists, and why three claims are not one
Which water filters are actually certified to reduce PFAS, and what does that certification cover?
Filters certified for trihalomethanes — 153 models, and four at the main
Which filters are certified to reduce TTHM, and should I treat the tap or the whole house?
Shower filters — one standard, one claim, and ten certified products
Do shower filters work, and is there a certified one for my water?
The VOC claim — one certification covering a printed list of compounds
What does a VOC reduction claim on a water filter actually cover?
What a whole-house filter is certified to do — and what it is not
What does a whole-house water filter actually remove, and is it worth the money?
10 pages
Private wells
I have a private well. Where do I start with treatment?
Well water treatment — what to test, in what order to treat
Test first, because nobody tests a private well for you and EPA's enforceable standards do not apply to one. Then treat in sequence: correct pH, remove iron and sulfur, soften, disinfect, and polish drinking water at the tap. Installing in the wrong order is what destroys equipment.
Acidic well water — blue-green stains, pinhole leaks and neutralisers
My well water is acidic. What damage is it doing and how do I correct it?
Arsenic in well water — why it is the one to test for deliberately
Should I test my well for arsenic, and what removes it?
Coliform bacteria in well water — what a positive test actually means
My well tested positive for coliform. What does that mean and what do I do?
Iron in well water — which filter actually removes it
Which iron filter do I need, given my iron level and the form it is in?
Manganese in well water — black stains, and the number nobody quotes
What causes black staining in my sinks and laundry, and what level is unsafe?
Nitrate in well water — do not boil it
My well has nitrate. What is the risk and how do I remove it?
Rotten egg smell in well water — find the cause before you buy anything
What causes the sulfur smell in my well water and how do I fix it?
Water hardness and softener sizing — the arithmetic, shown
Do I need a softener, and what capacity should I buy?
Well water testing — what to test for, and how to read the report
What should I test my well for, and what do the numbers on the report mean?
Start from the number, not the product
WaterSpec Lab is a reference for households choosing water treatment on evidence rather than on packaging. It is free, it sells nothing, and it names what it cannot tell you. If you have a test result, the sizing method turns it into a claim and a product form. If you do not, your annual report is the place to start and it costs nothing.