Pick the contaminant. Get the technology and the certification that covers it.
Every water filter recommendation should start with a standard, not a product. Choose what is in your water and this tells you which treatment technology is certified against it, the exact claim wording to look for in a certifier listing, and what will not work. Products come after that, and only where we can name the claim.
What are you trying to remove?
Buying a filter before testing is how people end up with the wrong technology. Three ways to find out what you actually have, cheapest first.
- Read your utility’s Consumer Confidence Report. Every community water system in the US has to publish one every year, and it names the disinfectant used and any contaminant that exceeded a limit. Find yours through the EPA.
- Look up your ZIP in a public database. The Environmental Working Group compiles utility test results by ZIP code. EWG Tap Water Database.
- Test at the tap. A report tells you what left the treatment plant. Lead, and anything else picked up from your own plumbing, only shows up in a sample taken at your own tap. Private wells are not covered by any report and need a certified lab test.
Once you have a result, come back and pick the contaminant it flagged.
The full mapping, on one page
Certification is granted claim by claim and model by model. A filter certified to a standard is not certified for everything in that standard, so the claim wording in the third column is the part that matters.
| Contaminant | Certified technology | Standard and claim to look for |
|---|---|---|
| PFAS | Reverse osmosis, activated carbon block, or non-regenerable anion exchange | NSF/ANSI 53 or 58. Claim: PFOA/PFOS reduction, or Total PFAS reduction. NSF/ANSI 401 does not cover PFAS. |
| Lead | Carbon block with a lead claim, or reverse osmosis | NSF/ANSI 53 or 58. Claim: Lead reduction. Tested from 150 ppb down to 5 ppb or lower. NSF/ANSI 372 is a materials standard, not a reduction claim. |
| Chlorine and chloramine | Activated carbon, catalytic carbon for chloramine | NSF/ANSI 42. Claim: Chlorine taste and odor reduction, or Chloramine reduction. Aesthetic standard, not a health claim. |
| Hard water | Cation exchange softener | NSF/ANSI 44. Claim: Hardness reduction. Salt-free conditioners control scale under IAPMO Z601 and do not soften water. |
| Bacteria and viruses | Class A ultraviolet, supplemental mechanical filtration, purifiers, or distillation | NSF/ANSI 55 Class A at 40 mJ/cm2, NSF/ANSI 244, NSF P231, or NSF/ANSI 62. Standards 53 and 58 allow only a protozoan cyst claim. |
| Arsenic | Reverse osmosis or adsorptive media | NSF/ANSI 58 or 53. Claim: Pentavalent arsenic reduction. Arsenic III has to be oxidized to arsenic V first. |
| Fluoride | Reverse osmosis, activated alumina, or bone char | NSF/ANSI 58 or 53. Claim: Fluoride reduction. Carbon block does not reduce fluoride. |
| Nitrate and nitrite | Reverse osmosis or anion exchange | NSF/ANSI 58 or 53. Claim: Nitrate/nitrite reduction. Separate from TDS reduction. |
| Microplastics | Filters holding the microplastics claim, or reverse osmosis | NSF/ANSI 401. Claim: Microplastics reduction, tested using the particulate method from NSF/ANSI 42. |
| Chromium-6 | Reverse osmosis or selective adsorptive media | NSF/ANSI 58 or 53. Claim: Hexavalent chromium reduction. A trivalent chromium listing does not cover it. |