A water softener and a water filter are often sold side by side, and they can sit next to each other on the same pipe. But they do different jobs. A softener removes hardness. A filter reduces other things, depending on what it is built and certified for. Which you need depends on what is in your water and what bothers you about it.
Install Water Softener is an independent referral service, not an installer or plumber. When you send the form, your details go to an independent local water treatment pro who can contact you and prepare a quote.
What a softener does
A softener removes calcium and magnesium, the minerals that make water hard, as water utilities describe it. A salt-based softener does it by ion exchange: resin beads swap the hardness for sodium or potassium, and are cleaned with brine from a salt tank. NSF/ANSI 44 is the standard for home softeners of this kind. A softener deals with scale, spots and soap scum. It is not designed to improve taste or remove contaminants such as lead.
What a filter does
Filter is a broad word. Different filters reduce different things, and the standard a filter is certified to tells you which. NSF/ANSI 42 covers aesthetic effects such as chlorine, taste and odor. NSF/ANSI 53 covers health effects such as lead. Reverse osmosis drinking water systems are covered by NSF/ANSI 58; EPA describes a point-of-use reverse osmosis system as one connected to a single fixture, such as under the kitchen sink.
| Water softener | Water filter | |
|---|---|---|
| Main job | Remove hardness (calcium, magnesium) | Reduce what it is certified for |
| Standard to look for | NSF/ANSI 44 | NSF/ANSI 42, 53, or 58 for reverse osmosis |
| Where it goes | Main line, whole house | Whole house or one tap |
| Helps with scale and soap scum | Yes | Not as its job |
| Helps with chlorine taste | Not as its job | If certified for it |
How to tell which you need
The Texas Commission on Environmental Quality gives advice that works anywhere: ask first what contaminant you want to remove or reduce, then choose a unit certified by NSF, UL or the Water Quality Association to remove that. Start from your symptoms and your water report.
- Spots, scale, soap scum, crust on fixtures: hardness. A softener.
- Chlorine taste or smell: a filter certified for chlorine, taste and odor.
- Reddish orange or black stains: iron or manganese, which EPA’s secondary guidelines link to staining. Tell the pro; it may need a filter, a softener set for it, or both.
- A health concern such as lead: a treatment certified for that contaminant, chosen from a test result.
- Several of these: both, in the order a pro suggests.
Using both
Some homes have a softener for hardness and a filter for something else. Whole house filters and softeners can share the main line; a drinking water filter or reverse osmosis unit can sit under the kitchen sink. The order on the main line depends on the filter and your water, so ask the pro which goes first and why. If you are having a softener installed, it is simpler to plan any whole house filter at the same visit; choose Softener plus a filter on the form.
Need a softener, a filter or both?
Common mix-ups
Three mix-ups are worth avoiding. A softener does not make water safer to drink: utilities say hard water is not a health hazard, and that a softener may not improve the safety of water. A filter certified only for taste and odor is not certified for lead; for lead, look for one certified under NSF/ANSI 53, which covers health effects such as lead. And a filter is not a softener: check that whatever you buy is certified for the problem you actually have. Reading the certification, not the label on the box, avoids buying the wrong thing.
Questions to ask before buying either
- What exactly does it remove or reduce, and to which standard is it certified?
- What does my water report or test say it needs to handle?
- Whole house or one tap: which fits what I want?
- Does it need a drain or power, and is there room for it near the main line or under the sink?
- How will I know it is working: what test, and how often?
- What upkeep does the maker ask for?
- If both, which goes first on the line, and why?
The Water Quality Association, wqa.org, also publishes information on home treatment systems, as some utility water reports point out. For the softener side, see how a softener works and the whole house installation page.
