A salt-based softener is the only one of the three that removes hardness from the water. A scale inhibitor or a “conditioner” leaves the calcium and magnesium in the water and tries to change how they form scale. If your water is soft, you need none of them. If it is moderately hard, an inhibitor or conditioner may be enough. If it is very hard, a softener is the option with the strongest evidence behind it.
First, find your number. Use the lookup page to find your city, or the calculator to turn your hardness into a sizing estimate.
What each device does
The three names are used loosely. Vendors mix them, so read the product description, not the label.
Ion-exchange softener. Resin beads swap calcium and magnesium for sodium (or potassium). The hardness is gone from the treated water. The resin is recharged (“regenerated”) with salt brine, which goes to a drain. You need a drain, power, salt and a service routine.
Scale inhibitor. Usually a cartridge with polyphosphate or a similar additive that dissolves slowly into the water. It aims to keep scale from sticking to pipes and heating elements. The hardness stays in the water. Cartridges need replacing on a schedule, and they work best in the cold line ahead of the heater.
Conditioner. This word covers two different things:
- Template-assisted crystallization (TAC) media, which turn dissolved hardness into tiny crystals that are less likely to stick.
- Magnetic, electronic or ultrasonic units, which claim to change how scale forms with no media at all.
Some sellers also call a softener a “water conditioner”. If a product says “conditioner” and also says it needs salt and a drain, it is a softener.
How strong is the evidence?
For softeners, the mechanism is simple chemistry and the result is easy to check: the treated water tests soft.
For inhibitors, conditioners and physical devices, the result is a reduction in scale, not the removal of hardness. Results vary by product and by water. A 2007 trade-press review in Water Conditioning & Purification called physical treatment promising but unproven, and noted that few devices pass Germany’s DVGW W 512 test protocol. It also noted that no US test standard existed at that time. A later article in WaterWorld describes IAPMO/ANSI Z601, published in 2018, which tests scale-reduction devices against untreated control stations. Look for a product that has passed an independent test like this, not a vendor’s own brochure.
We cannot verify vendor performance claims, and we do not use them.
Comparison
| Softener | Scale inhibitor | TAC conditioner | Magnetic / electronic | |
|---|---|---|---|---|
| Removes hardness | Yes | No | No | No |
| Prevents scale | Yes, in treated water | Reduces it | Reduces it | Unproven |
| Salt and drain | Yes | No | No | No |
| Consumable | Salt, resin over years | Cartridge | Media, long life | None |
| Soap lather and spotting | Improves | No change | No change | No change |
| Best for | Hard and very hard water | Moderate water, protecting a heater | Moderate to hard water, no drain available | Little to recommend yet |
The soap and spotting row matters. Hardness itself affects how soap lathers and how glasses spot. Inhibitors and conditioners do not change that, because the hardness is still there.
Choosing by hardness
These are rules of thumb, not a standard. They use the USGS classes: soft up to 60 mg/L, moderately hard 61–120, hard 121–180, very hard above 180 mg/L as calcium carbonate.
- Soft (up to 60 mg/L). Skip all three. New York averages 32 mg/L (1.9 gpg) and Charlotte also 32 mg/L (1.9 gpg). Sheffield is reported at 42 mg/L. Scale is minor.
- Moderately hard (61–120 mg/L). An inhibitor on the heater feed is a reasonable low-cost step. Austin averages 93 mg/L (5.4 gpg) and Houston 110 mg/L (6.4 gpg).
- Hard (121–180 mg/L). This is the grey zone. Columbus is 123 mg/L (7.2 gpg), Los Angeles 128 mg/L (7.5 gpg), Leeds 135.6 mg/L and Philadelphia 152 mg/L (8.9 gpg). A softener gives a clear result. A conditioner may cut scale at lower cost, but the benefit varies.
- Very hard (above 180 mg/L). Phoenix is 237 mg/L (13.9 gpg), San Diego 239.5 mg/L (14.0 gpg) and Indianapolis 317 mg/L (18.5 gpg). A softener is the usual answer. An inhibitor or conditioner may not keep up.
City figures are not your tap
Many figures on this site are a median across several supplies. Your street can sit well away from it.
- Los Angeles is a median across six supplies, with a range of 78 to 280 mg/L.
- San Diego ranges from 54.4 to 285 mg/L, depending on which plant feeds the area.
- Philadelphia ranges from 81 to 220 mg/L, depending on the treatment plant.
- Leeds ranges from 112.9 to 169.3 mg/L.
Check your supplier’s page for your address before you buy. If the figure sits near a boundary, ask the supplier for the latest analysis.
Practical points
- A softener is sized for hardness, household size and water use. The calculator gives a starting estimate.
- Softened water is not meant for every tap. Many households keep an unsoftened cold line for drinking. Ask your installer.
- If you rent, an inhibitor cartridge or a descaling routine is often the only option you can fit without plumbing changes.
- Whatever you install, check the result. A simple test strip for hardness before and after costs little and shows whether the device works.
FAQ
Will a conditioner stop limescale on my kettle? Not reliably. A conditioner or inhibitor can reduce scale in pipes and heaters, but the hardness remains in the water, so a kettle that boils the water can still scale. Test results vary by product and water.
Is a “salt-free softener” a softener? No. A salt-free unit does not remove calcium or magnesium. It is an inhibitor or a conditioner. The water measures just as hard after it as before.
My water is only moderately hard. Do I need anything? Probably not a softener. Descale kettles and shower heads as needed, and consider an inhibitor on the heater feed if your heater is costly to replace. Compare your city on the lookup page first.
Sources
- USGS, Water Science School: Hardness of water
- Karen R. Smith, Water Conditioning & Purification, 2007: Can physical water treatment prevent and control scale?
- WaterWorld: Testing for scale
- NYC DEP: 2025 Drinking Water Supply and Quality Report
- LADWP: 2025 Drinking Water Quality Report
- Citizens Energy Group: 2025 Water Quality Report
- City of Phoenix: Water quality report
- Yorkshire Water: domestic drinking water quality open data