Water Filter vs Water Softener: Which Do You Need?

What is the difference between a water filter and a water softener?

A water filter removes contaminants like chlorine, sediment, lead, and VOCs (NSF/ANSI 42, 53, 401). A water softener removes hardness minerals (calcium and magnesium) through ion exchange (NSF/ANSI 44). Filters improve taste and remove contaminants. Softeners prevent scale and improve soap performance.

Water Filters

A water filter removes physical particles, chemicals, and contaminants from water. Different filter types target different contaminants.

Types of Water Filters

Sediment Filter

Removes sand, silt, rust, and particles. Typically 5-20 micron rating. Does not remove chemicals, chlorine, or hardness. Used as a prefilter for other systems.

Activated Carbon Filter

Removes chlorine, taste, odor, and some VOCs. NSF/ANSI 42 certified for aesthetic contaminants. Does not remove hardness, bacteria, or heavy metals. Best for city water with chlorine.

Catalytic Carbon Filter

Removes chloramine (more persistent than chlorine). NSF/ANSI 42 and 53 certified. Used in whole-house systems like Aquasana Rhino. Does not remove hardness.

Reverse Osmosis (RO)

Removes nearly all contaminants including hardness, heavy metals, and dissolved solids. Typically used at point-of-use (under sink). Not practical for whole-house due to flow rate and wastewater.

What Water Filters Do NOT Do

Water Softeners

A water softener removes hardness minerals (calcium and magnesium) through ion exchange. Soft water prevents scale buildup and improves soap performance.

How Water Softeners Work

Hard water flows through a resin tank where calcium and magnesium ions are exchanged for sodium or potassium ions. The system regenerates periodically using salt brine to recharge the resin and flush hardness minerals down the drain. NSF/ANSI 44 certified systems are verified to remove hardness.

What Water Softeners Do NOT Do

Do You Need Both?

Many households benefit from both a filter and a softener, depending on water source and quality.

City Water with Chlorine and Hardness

Install both: a carbon filter to remove chlorine and improve taste, and a softener to remove hardness. Combo systems like SoftPro Elite include both a softener resin tank and a carbon filter tank.

City Water with Chlorine, Low Hardness (<7 GPG)

You only need a carbon filter. Hardness below 7 GPG is considered soft to moderately hard and does not require softening. A catalytic carbon system like Aquasana Rhino removes chlorine and contaminants without the expense of a softener.

Well Water with Iron and Hardness

You need an iron removal system (oxidation filter or greensand) followed by a softener. Iron must be removed first — softener resin cannot handle iron and will foul. Add a sediment prefilter to protect both systems.

Well Water with Low Hardness and No Iron

You may only need a sediment filter and UV sterilizer (for bacteria). Well water without hardness or iron does not require softening or iron filtration. Test annually to monitor changes.

Installation Order

When installing multiple systems, the correct order matters:

  1. Sediment prefilter (5-20 micron) — protects downstream equipment
  2. Iron/manganese filter (if needed for well water) — must come before softener
  3. Water softener — removes hardness after contaminants are filtered
  4. Carbon filter (optional) — removes chlorine or improves taste after softening
  5. UV sterilizer (if needed for bacteria) — comes last after all filtration

How to Choose

Start with a Water Test

Test for hardness (GPG), iron, manganese, chlorine, pH, TDS, and bacteria. City water reports are available from your municipality. Well water should be tested annually by a certified lab.

Match Your System to Your Water

Common Mistakes

See Also

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