The U.S. water filter market generates over $4 billion a year, but most consumers don't know that a filter effective against lead may do nothing for PFAS, and vice versa. The key is matching filter technology to the specific contaminants in your water.
Step 1: Know What's in Your Water
Before buying any filter, check your water system's violations and consumer confidence report on SafeWater →. If you're on a well or concerned about lead from household plumbing, get a lab test first.
The NSF/ANSI Certification System
NSF International sets independent standards for water treatment devices. Look for these certifications:
- NSF/ANSI 42: Aesthetic effects (chlorine taste/odor, sediment)
- NSF/ANSI 53: Health effects: lead, VOCs, cysts (Giardia, Cryptosporidium)
- NSF/ANSI 58: Reverse osmosis systems; covers most heavy metals and PFAS
- NSF/ANSI 244: Microbiological reduction (bacteria, viruses)
- NSF/ANSI 473: Emerging contaminants including PFOA and PFOS
A filter can claim "reduces contaminants" without NSF certification. Always verify at nsf.org.
Filter Technologies Compared
Activated Carbon (AC / GAC)
Removes: Chlorine, VOCs, some pesticides, some PFAS (especially longer-chain), taste/odor
Does NOT reliably remove: Lead, nitrates, arsenic, most heavy metals, fluoride, hardness minerals
Best for: General taste improvement; PFAS reduction when certified under NSF 473
Reverse Osmosis (RO)
Removes: PFAS (90–99%), lead (up to 99%), arsenic, nitrates, fluoride, most dissolved solids
Limitations: Wastes 3–4 gallons per gallon filtered; removes beneficial minerals too; requires undersink installation
Best for: Broad contaminant removal; PFAS and heavy metals
Ion Exchange / Water Softeners
Removes: Hardness minerals (calcium, magnesium), some heavy metals
Does NOT remove: PFAS, bacteria, viruses, nitrates
Best for: Hard water; often combined with RO for full contaminant coverage
UV Purification
Removes: Bacteria, viruses, protozoa (Giardia, Cryptosporidium)
Does NOT remove: Any chemical contaminants
Best for: Well water with microbiological concerns; always pair with a carbon filter
Ceramic / Mechanical Filters
Removes: Sediment, some bacteria, cysts
Best for: Pre-filtration; turbid well water
Contaminant-to-Filter Cheat Sheet
| Contaminant | Best Filter | NSF Cert |
|---|---|---|
| Lead | RO or AC block | NSF 53 or 58 |
| PFAS (PFOA/PFOS) | RO or certified AC | NSF 58 or 473 |
| Nitrates | RO or ion exchange | NSF 58 |
| Arsenic | RO or activated alumina | NSF 58 or 53 |
| Bacteria/Viruses | UV + carbon | NSF 244 |
| Chlorine/Taste | Any GAC or AC | NSF 42 |
Related: Do Water Filters Remove PFAS? What Actually Works →