Water Softener vs Water Filter: What Each One Actually Does

A water softener removes the minerals that cause hard water, mainly calcium and magnesium, to stop scale and spots. A water filter removes other things, such as sediment, chlorine, taste, odor and some contaminants. They solve different problems, so test your water first and buy the one that matches your problem.

People mix these two up all the time, and sellers do not always help. Choosing the wrong one means spending hundreds of dollars and still having the same problem. This guide explains what each does, what it does not do, and how to decide.

What does a water softener do?

A softener deals with hardness, which is dissolved calcium and magnesium. Hard water leaves:

• White, chalky scale on faucets and showerheads
• Spots on glasses and dishes
• Soap that does not lather well
• Scale in the water heater, pipes and appliances
• Dry skin and stiff laundry for some people

Most home softeners use ion exchange. Hard minerals stick to resin beads, and the water leaves softer. The beads need to be recharged with salt from time to time. A softener is built for hardness. As one source puts it, it does not remove contaminants beyond the hardness minerals.

What does a water filter do?

A filter removes particles or chemicals from water. What it removes depends on the type:

Check the product's certification and the list of contaminants it is rated for. A filter does not soften water. The scale problem stays.

Softener vs filter: side-by-side

Which problem do you have?

• White crust, spots, dry skin, weak lather: hard water. Think softener.
• Chlorine smell or taste: a carbon filter.
• Cloudy water or visible grit: a sediment filter.
• Orange or brown stains: possibly iron. Look at an iron filter.
• Rotten egg smell: this is often a hydrogen sulfide or water heater issue. See why your water smells like rotten eggs.
• Worried about specific contaminants such as lead: do not guess. Use a certified filter and test your water with a lab.

How to test your water first

1. Get your utility's water quality report. In the United States, public water systems publish a yearly consumer confidence report. It often lists hardness.
2. Use a test strip kit from a hardware store for a quick hardness reading.
3. Use a lab test if you have a private well. Well water is not tested by a utility.
4. Look at the signs around the house, such as scale and stains.

Hardness is often given in grains per gallon (gpg) or milligrams per liter. Higher means harder. A local water professional can tell you what counts as hard in your area.

When do you need both?

Both is the right answer when the water is hard and also has other issues, such as chlorine taste or sediment. Many homes install a sediment or carbon filter first, then a softener. Order matters because particles and chlorine can damage softener resin over time. Ask the installer for the right order for your water. Some sellers push combination systems, so compare quotes and ask for your test results to be used.

Is soft water safe to drink?

Softened water has a little more sodium, because the process swaps hardness minerals for sodium or potassium. For most people the amount is small. If you are on a low-sodium diet, ask your doctor. Many households keep one tap unsoftened or use a filter at the kitchen sink for drinking.

What about installation and cost?

Costs vary a lot by region, brand and plumbing layout, so get at least two written quotes. A softener or whole-house filter usually needs a plumber for the main line. If you are comfortable with DIY plumbing and local code allows it, our guide on installing a whole-house filter covers the steps.

Whole-house systems can also hide leaks, so after installation check every connection and watch the meter. See finding hidden leaks for how.

Common mistakes

• Buying a softener to fix taste. It will not remove chlorine.
• Buying a filter to stop scale. It usually will not.
• Skipping the water test.
• Forgetting maintenance. Softeners need salt. Filters need changing on schedule or they stop working and can grow bacteria.
• Believing marketing claims without certification.

Bottom line

Softener for scale and spots, filter for taste, particles and contaminants. Test first, match the tool to the problem, and add the second one only if the test shows you need it.