Salt is the running cost nobody prices before buying a softener, and the bag wall invites spending more than the chemistry justifies. Almost every bag is sodium chloride, all of it softens identically, and what separates bags is purity, form, and price. This guide compares types on manufacturer purity figures, shows how much a correctly sized system uses, and prices a year of each. We have not hands-on tested any salt; we checked data sheets and listings, and show the math.
Disclosure: TapChecked is reader-supported. If you buy through links on this page we may earn a commission, at no extra cost to you. It never changes which products we pick or how we rank them. See how we check and our full disclosure.
First, how much salt a softener actually uses
Salt does not soften water; resin does. Salt only regenerates the resin, so use is set by daily grains (people × 75 gallons × compensated hardness — see our how to size a water softener guide), regeneration frequency, and dose. At the efficient dose our softener sizing calculator assumes — about 6 pounds per cubic foot — a 48,000-grain system with 1.5 cubic feet uses 1.5 × 6 = 9 pounds per regeneration. Weekly: 9 × 52 = 468 pounds a year; 468 ÷ 40 = 11.7, about 12 bags; at around $8 a bag, about $96 a year. “A bag or two a year” for a family on hard water fails this arithmetic — and so does a bag a week.
The types, compared
| Type | Purity (maker figures where published) | 40-lb bag, around | Bridge / mush risk | Best for |
|---|---|---|---|---|
| Evaporated pellets | 99.65% min. (Morton data sheet) to 99.8% (Diamond Crystal) | $8–$10 | Lowest | The default for most systems |
| Solar crystals | 99.5% min. (Morton) to typically 99.6% (Diamond Crystal) | $7–$11 | Moderate; more in humid spaces | Good value on municipal water, moderate use |
| Rock salt | About 95–98% (approximate; no maker sheet found) | $5–$8 (approximate) | Highest; insoluble sludge builds up | Rarely worth the saving |
| Block salt | High-purity compressed salt (a form, not a purity class) | Not sold in comparable 40-lb bags | Low in systems designed for it | Only block-fed designs (see below) |
| Potassium chloride pellets | About 99% | $45–$55 (Morton 40 lb listed at $47.28 at Lowe’s) | Higher; can harden in cold, humid spots | Sodium must be avoided |
Prices checked November 2026: Morton pellets $9.99 at Target, Diamond Crystal Solar Naturals $10.49 at Tractor Supply; warehouse stores often run lower. Treat prices as “around” — salt is heavy, regional, and promoted often.
Evaporated pellets: the default
Brine is evaporated and compressed into pellets — the purest common form. Morton’s data sheet puts Clean and Protect at a 99.65 percent minimum sodium chloride, 0.1 percent maximum insolubles; Cargill rates Diamond Crystal Bright & Soft at up to 99.8 percent. Purity is not a softening advantage — the resin cannot tell — it is housekeeping: almost everything dissolves, little sludge accumulates, and pellets are least prone to the tank failures below. At a dollar a bag over crystals and twelve bags a year, the premium is about $12 a year. That is the whole case, and for most owners it suffices. Data sheets: Morton, Diamond Crystal.
Solar crystals: the value option, with a humidity caveat
Solar salt is brine evaporated in open ponds by sun and wind, harvested as crystals. Morton rates its solar crystals at 99.5 percent minimum; Cargill rates Solar Naturals at typically 99.6 percent — close to pellets, and in a dry room solar crystals work well for years. The caveats are form and climate: loose crystals dissolve less evenly, and in humid basements they are more prone to bridging — a crust over a hollow above the brine, so the tank looks full while no salt dissolves — and to mushing, where re-crystallised salt compacts into sludge that chokes brine draw. Morton screens its crystals to limit fines specifically to reduce bridging, which tells you the risk is real. Dry space, moderate use: save the money. Damp basement, high use: pellets.
Rock salt: the saving that costs a cleanout
Rock salt is mined and crushed with minimal processing, and is the cheapest bag on the shelf. Its insoluble fraction — calcium sulfate and other minerals, roughly 2 to 5 percent on approximate figures — never dissolves; it settles as sludge that can foul the brine well and float valve. In numbers: at 470 pounds a year, pellets at 99.8 percent purity leave about 470 × 0.002 = roughly 1 pound of insolubles; rock salt at 96 percent leaves about 470 × 0.04 = roughly 19 pounds. Saving perhaps $2 × 12 bags = $24 a year buys that sludge. Some manuals say do not use it at all — Kenmore directs owners to nugget or pellet salt and warns rock salt’s dirt will stop the softener working.
Block salt: a form for specific machines
Block salt is compressed salt in blocks that slot into a brine compartment built for them — the standard fill for many compact twin-cylinder designs (Harvey and TwinTec cabinets, many Kinetico models in the UK market). It is not interchangeable with loose salt: blocks will not feed a standard open tank, and loose salt can jam a block-fed cabinet. Most US softeners take loose fill, so this is a non-question unless your manual names it.
Potassium chloride: the sodium-free alternative, honestly priced
Potassium chloride (KCl) regenerates resin with potassium instead of sodium. It is legitimate for a medical sodium restriction, or where sodium in discharge is the concern. Price it plainly: a 40-pound bag of Morton KCl was listed at $47.28 at Lowe’s, against around $9 to $10 for sodium pellets — roughly five times the price, before efficiency. Efficiency widens the gap: KCl has fewer exchange ions per pound, and manufacturers tell you to compensate — GE Appliances advises setting hardness 20 percent higher with KCl, Kenmore manuals 25 percent where there is no KCl setting — so plan on 20 to 25 percent more by weight. Standard household: 468 lb × 1.25 = 585 lb a year; 585 ÷ 40 = about 15 bags; 15 × around $47 = about $705 a year, versus about $96 in salt. KCl can harden in cold, humid tanks (Kenmore advises at most about 60 pounds in the tank). Buy it for a reason, not a vague health upgrade — and anyone with a potassium-related condition should check with their clinician first.
Annual cost for three household sizes
Each row: daily grains from the sizing method, a system sized at 70 percent of rating, 6 pounds per cubic foot per regeneration. Salt at around $8 a bag; potassium at around $47 with the 25 percent uplift, bags rounded up.
| Household | System and dose | Regenerations / year | Salt / year | Bags / year | Cost: salt / potassium |
|---|---|---|---|---|---|
| 2 people, 10 gpg, 0.5 ppm iron | 24,000 grains, 0.75 cu ft, 4.5 lb; 16,800 delivered ÷ 1,875 = every ~11 days | About 33 | 33 × 4.5 = ~149 lb | About 4 | About $32 / about $235 |
| 4 people, 15 gpg | 48,000 grains, 1.5 cu ft, 9 lb; about weekly | About 52 | 52 × 9 = 468 lb | About 12 | About $96 / about $705 |
| 6 people, 20 gpg | 80,000 grains, 2.5 cu ft, 15 lb; 56,000 delivered ÷ 9,000 = every ~6 days | About 61 | 61 × 15 = ~915 lb | About 23 | About $184 / about $1,365 |
Two lessons: salt cost scales with hardness and people, not softener price — the big household spends in a year what the small one spends in six — and timer valves can waste much of these figures; a metered valve is the cheapest salt-saver in the system. Our best water softener systems guide builds these households into five-year totals; the water softeners hub collects the rest.
Storage, handling, and the monthly two-minute check
- Keep it dry and sealed. Humidity triggers bridging. Store bags off a damp floor and reseal an opened bag.
- Keep the tank roughly one-third to two-thirds full. Running empty risks hard water; overfilling invites a bridge. Top up a bag at a time.
- Check monthly. Tap suspect salt with a broom handle — a hollow sound means a bridge. A level that never falls is a fault, not a saving.
- Lift honestly. Consider 25-pound bags, at a worse per-pound price, if that keeps the tank filled.
When high-purity salt actually matters
For modest city-water use, 99.5 versus 99.8 percent purity is a few pounds of residue over years — buy on price and form. High purity earns its premium where volume or chemistry multiplies residue: homes pushing 500-plus pounds a year, frequent regeneration, and iron-bearing well water, where iron-fighting pellets (with a resin-cleaning or iron-complexing additive, such as Diamond Crystal’s Iron Fighter line) can help keep resin cleaner with low clear-water iron. But additive salt is housekeeping, not iron treatment: at roughly 1 ppm of iron and above, plan on dedicated iron filtration.
And if your system needs no salt at all
Salt-free conditioners use no salt or regeneration, because they do not remove hardness; they change its scale behaviour. Before choosing one to escape the salt bill, read our salt-based vs salt-free softeners explainer: the $30 to $185 a year in salt buys water that actually tests soft.
Frequently asked questions
Can I mix salt types, or switch from crystals to pellets?
Yes for sodium chloride forms — let the level run low first. Switching to or from potassium chloride also works: run the old regenerant low, adjust hardness up about 20 to 25 percent for KCl (back down for salt), and follow your manual.
How long does a 40-pound bag last?
From the math above: the four-person, 15 gpg household uses about 468 pounds a year — a bag roughly every month. Two-person homes: a bag about every three months. Large, very-hard-water homes: two a month. Any universal answer ignores hardness.
Is expensive salt better for my softener?
Only in housekeeping. Purity buys a cleaner tank and fewer bridges — not softer water or extra capacity. The verified gap between solar crystals (99.5–99.6 percent) and premium pellets (99.65–99.8 percent) is small; the gap to rock salt’s insolubles is what matters.
What is a salt bridge, and how do I fix one?
A bridge is a hard crust above the brine, with a hollow underneath: no brine forms, regeneration fails, and the tank still looks full. Break it gently with a broom handle and check monthly. Prevention: dry storage, no overfilling, and — in humid spaces — pellets.
Can I use ice-melt, pool, or table salt instead?
No. Ice-melt carries insolubles a brine system handles worst, pool salt is for chlorinators, and table salt’s fine grains invite mushing. Manuals specify softener salt. The saving is small; the cleanout is yours.
The bottom line
Buy evaporated pellets for the cleanest default, solar crystals if your space is dry and the price gap is real, and potassium chloride only when sodium itself is the problem — at roughly seven times salt’s annual cost for the same soft water. Skip rock salt. Then spend attention where it pays: a metered valve, a correct hardness setting from our sizing guide and calculator, and a monthly look in the tank. Salt choice is a $10 decision; sizing and settings are the $100 ones.