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Filters and softeners do different jobs
NSF/ANSI 42 covers filters that reduce aesthetic issues like chlorine, taste and odor. NSF/ANSI 53 covers specific health-related contaminants named in the product listing.1 Hardness reduction is what NSF/ANSI 44, the standard for cation-exchange softeners, covers.2 So a filter certified only to 42 or 53 isn't certified to soften water.
Where RO fits
NSF/ANSI 58 point-of-use RO systems are tested for TDS reduction.3 That improves drinking water at one tap, but it won't protect your water heater or fixtures from scale.
Costs compared
| System | Installed (HomeGuide) |
|---|---|
| Under-sink filter | $170–$5804 |
| Whole-house filtration | $850–$5,4004 |
| Salt-based softener | $1,200–$3,8005 |
Quick pick
- Scale, spots, appliance wear: softener
- Chlorine taste or odor: carbon filter (NSF/ANSI 42)
- Drinking-water quality: RO (NSF/ANSI 58)
More: whole-house filter cost · signs you need a softener
Sources
- NSF: NSF/ANSI 42, 53 and 401 filtration standards
- NSF: NSF/ANSI 44 technical requirements
- NSF: NSF/ANSI 58 reverse osmosis systems
- HomeGuide: home water filtration system cost (2026)
- HomeGuide: water softener cost, including ongoing salt and maintenance costs (2026)
Last reviewed Oct 13, 2026. This is general information, not professional advice. Confirm figures with your utility and installer.