Filters
Water softener vs water filter: what each does
A water softener swaps hardness minerals (calcium and magnesium) for sodium or potassium and is certified under NSF/ANSI 44. A filter removes particular contaminants and is certified under 42, 53 or 401. A softener is not a PFAS or lead filter, and a filter does not soften water.
Two different jobs
Softener. According to EPA WaterSense, softening water with a cation exchange softener removes excessive hardness. It exchanges the hardness ions for others, and regenerates with salt brine. EPA says softeners should be certified to NSF/ANSI 44, which includes a voluntary efficiency rating of 5.0 gallons of water or fewer per 1,000 grains of hardness removed.
Filter. Filters trap or remove contaminants using media such as activated carbon, ion exchange resin or fabric and ceramic barriers. They are certified for specific claims under NSF/ANSI 42 (aesthetic effects such as chlorine), 53 (health effects such as lead) or 401 (emerging compounds), and RO systems under 58.
Quick comparison
| Softener | Filter | |
|---|---|---|
| Target | Hardness (calcium, magnesium) | Specific contaminants on its listing |
| Standard | NSF/ANSI 44 | NSF/ANSI 42, 53, 401 (RO: 58) |
| Where | Usually whole house | Usually at one tap; also whole house |
| Uses water or salt | Yes, regenerates with brine and discharges salts | Carbon filters do not consume water; RO does |
| PFAS | Not likely to remove | Some certified to reduce PFAS |
| Lead | Not a lead treatment | Some certified for lead |
Why a softener is not a PFAS or lead fix
The Minnesota Department of Health says softeners and iron filtration “are not likely to remove PFAS” and that sampling data show whole-house softening and iron filtration systems do not remove PFAS. Lead is a different problem: it enters at pipes and fixtures, so a treatment that works on the incoming water cannot affect lead picked up inside the house, and EPA’s lead guidance points to certified filters at the tap and flushing.
When you might want both
If your water is hard and you also want a contaminant reduced at the tap, the two can be combined, for example a whole-house softener plus an under-sink carbon or RO unit certified for the contaminant. EPA WaterSense points out that softeners discharge salts and can affect local water quality, and that hardness-related signs include scaly residues and soap that does not lather (EPA’s well-water guide lists those clues and says to test for hardness).
Choosing
- If you see scale on fixtures or soap does not lather, ask your utility for the hardness figure and look for a softener certified to NSF/ANSI 44 with a high efficiency rating.
- If you are worried about a contaminant, identify it first from your utility’s data or a lab test, then match a filter listing to it (certifications).
Sources
Not medical or legal advice. This guide summarizes public documents so you can ask better questions of your utility, your health department or a certified lab. For health concerns, talk to a clinician; for compliance questions, to your state drinking water program. Pages on this site that name products may earn a commission, as disclosed on the affiliate disclosure page.