A water softener removes calcium and magnesium from your water by ion exchange: resin beads swap the hardness minerals for sodium (or potassium), and a salty brine recharges the beads every few days. For a typical home the decisions are whether you need one, what size, and which type, and the running cost is mostly salt: about $76 a year for a family of four on 10 gpg water with an efficiency-rated unit.
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This guide covers how softeners work, the main types, what efficiency ratings mean, sizing, running costs and the downsides, with links to our detailed guides on each step.
How a water softener works
Inside the tall tank is a bed of small plastic resin beads. PNNL’s Building America Solution Center describes the process: as hard water passes through, calcium and magnesium ions are swapped for sodium, potassium or hydrogen ions held on the resin. When the beads are saturated with hardness, they’re regenerated with concentrated brine (sodium or potassium chloride), which pushes the hardness off the beads, and the spent solution goes down the drain.
- Service: water flows through the resin and comes out soft.
- Backwash: water flows upward to loosen the bed and flush out debris.
- Brine draw: brine from the salt tank is pulled through the resin, recharging it.
- Rinse and refill: excess brine is rinsed out and the salt tank refills with water for next time.
On Pentair’s whole-house models a regeneration takes up to about two hours, and the house gets unsoftened water while it runs, which is why it’s scheduled for the small hours.
Types of water softener
| Type | How it decides to regenerate | Removes hardness? | Notes |
|---|---|---|---|
| Demand-initiated (metered) | After a set volume, from a flow meter or sensor | Yes | Required for the NSF/ANSI 44 efficiency rating |
| Timer (time-clock) | On a fixed schedule | Yes | PNNL notes this can mean unnecessary regeneration and wasted water |
| Twin-tank | Metered; one tank works while the other regenerates | Yes | Soft water around the clock; for heavy use or very hard water |
| Potassium chloride instead of salt | As above | Yes | No sodium added; Culligan says it’s more expensive and less efficient |
| Salt-free conditioner | No regeneration | No | Changes minerals so they scale less when heated (Wessex Water); results vary |
| Tank exchange service | Tank swapped and recharged off-site | Yes | No brine to your drain (MPCA) |
Efficiency ratings: what to look for
Every residential softener sold in the US must meet the general requirements of NSF/ANSI 44 (or the equivalent WQA S-100), according to PNNL. The standard’s optional efficiency rating goes further. To qualify, a softener must:
- remove at least 3,350 grains of hardness per pound of salt;
- use no more than 5 gallons of water per 1,000 grains removed;
- be demand-initiated, not on a timer.
Look for the efficiency rating on the spec sheet or in WQA, NSF or UL listings. It matters because efficiency depends heavily on the salt setting: Pentair’s data for its smallest whole-house model shows 4,272 grains per pound at its lowest salt dose but only 1,945 at its highest. Our guide to how much salt a water softener uses explains the trade-off.
Do you need one?
Start with your hardness. Below about 3.5 gpg (60 mg/L) there’s nothing worth removing; above about 7 gpg (120 mg/L), and especially above 10.5 gpg, scale becomes a real cost for water heaters, dishwashers and fixtures. The USGS describes hardness as a nuisance rather than a health concern, so this is a practical decision. Work through our do I need a water softener checklist, and find your figure in the water hardness by city table or your utility’s report.
What size do you need?
Multiply by 7 for a weekly regeneration and choose a size that covers it at a medium salt setting, where softeners deliver about 80% of their rated capacity. A family of four on 10 gpg water removes 3,200 grains a day, or 22,400 a week, which points to a 32,000-grain unit. Use the calculator for your numbers:
This calculator needs JavaScript. Use the formula above.
More detail, tables and worked examples: what size water softener do I need and how often a softener should regenerate.
Running costs
For a family of four at 80 gallons each a day, with an efficiency-rated softener and salt at $8.76 per 40 lb bag (Walmart, October 2026):
| Hardness | Salt per year | Salt cost | Regeneration water (max.) |
|---|---|---|---|
| 5 gpg | 174 lb | $38 | 2,920 gal |
| 10 gpg | 349 lb | $76 | 5,840 gal |
| 15 gpg | 523 lb | $115 | 8,760 gal |
| 20 gpg | 697 lb | $153 | 11,680 gal |
Downsides to weigh
- Sodium. Softening adds about 0.46 mg of sodium per mg of hardness removed (Vermont Department of Health), roughly 7.9 mg/L per gpg (Morton). Ask your doctor if you’re on a sodium-restricted diet, and consider an unsoftened kitchen tap.
- Chloride in waterways. Brine goes down the drain. The MPCA reports 68 Minnesota lakes and streams over its chloride standard and promotes efficient softeners; some places restrict salt-based softeners, so check local rules.
- Maintenance. Monthly salt checks, the occasional salt bridge, and settings to keep right. See water softener maintenance.
- Not a filter. A softener removes hardness (and some iron), not chlorine taste, lead or bacteria. If you need those treated, you need a different system.
Installing and setting up
- Choose a demand-initiated, efficiency-rated model sized for your household.
- Keep outdoor taps on hard water, as the MPCA suggests, and consider leaving the kitchen cold tap unsoftened.
- Set the hardness to your water’s figure in gpg (high end of any range), plus 5 per ppm of iron: hardness setting guide.
- Start on the medium salt setting and check how often it regenerates after a few weeks.
- Test the softened water with a strip, and descale any appliances that already have scale: how to remove limescale.
Frequently asked questions
Does a water softener make water safe to drink?
A softener isn’t a safety device; it only removes hardness minerals. Softened water is drinkable for most people, with extra sodium.
How long does a regeneration take?
Up to about two hours on Pentair’s whole-house models.
Are salt-free water softeners real softeners?
Not in the strict sense: they don’t remove calcium and magnesium. Wessex Water and the MPCA describe them as conditioners that change how minerals behave.
What does a water softener cost to run?
Mostly salt: from about $38 a year at 5 gpg to $153 at 20 gpg for a family of four with an efficient unit, plus regeneration water.
