Use either rock salt or solar salt, depending on your softener's design and your water hardness level

Water softeners need salt to regenerate — to flush out the minerals they've trapped and get ready to soften more water. You have two main choices: rock salt and solar salt. Rock salt is cheaper and works in any softener, but it leaves more sediment behind. Solar salt costs more but dissolves cleaner and works better if your water is very hard or your softener sits in a cold climate. A third option, evaporated salt, exists but is rarely stocked at hardware stores and costs significantly more.

The salt you pick matters because the wrong type can clog your softener's brine tank or reduce how often you need to refill it. Most softeners work with any of these types, but some newer models specify which one to use. Check your owner's manual before buying — the brand name and model number are usually on a sticker inside the cabinet door.

Key Takeaways

  • Rock salt is the cheapest option and works in any softener, but leaves sediment that requires more frequent tank cleaning.
  • Solar salt dissolves more completely, lasts longer between refills, and works better in very hard water or cold climates.
  • Your softener's manual will tell you which type it was designed for, and some newer models require a specific kind.
  • Salt pellets are easier to handle than crystals or blocks, and most hardware stores stock them in 40-pound bags.
  • Never use table salt, kosher salt, or any salt with anti-caking agents — these will damage your softener.

Rock salt: cheaper but dirtier

Rock salt comes straight from underground salt deposits with minimal processing. It costs the least — usually $4 to $6 per 40-pound bag — and you can find it at any hardware store, big-box retailer, or feed supply. It works in every softener on the market.

The downside is that rock salt contains insoluble minerals and clay. When you add it to the brine tank, not all of it dissolves. The leftover sediment settles at the bottom and builds up over time. If you ignore it, the sediment can block the brine line or prevent the softener from regenerating properly. You'll need to clean out the tank every one to three years, depending on how hard your water is and how much salt you use.

Rock salt makes sense if your water hardness is mild to moderate (under 15 grains per gallon) and you don't mind the occasional tank cleaning. It's also the only choice if your budget is tight or your softener is very old.

Solar salt: cleaner and longer-lasting

Solar salt is made by evaporating seawater or brine in shallow ponds under the sun. It's purer than rock salt — about 99.5% sodium chloride — so it dissolves almost completely in the brine tank. You'll rarely see sediment buildup, and you can go three to five years between cleanings.

Solar salt also lasts longer between refills. Because it dissolves so cleanly, your softener can use it more efficiently, meaning you won't need to add salt as often. This matters most if your water is very hard (over 15 grains per gallon) or if you live somewhere cold — in freezing climates, rock salt can clump and won't dissolve properly, while solar salt performs better.

The trade-off is price. Solar salt costs $8 to $12 per 40-pound bag, roughly double what rock salt costs. Over a year, the difference adds up, but you save time on maintenance. If your softener is newer or if your water is very hard, solar salt usually pays for itself.

Evaporated salt: the premium option you probably won't find

Evaporated salt is the purest form — over 99.9% sodium chloride — and dissolves completely with zero sediment. It's the best choice for softeners in very cold climates or homes with extremely hard water.

The problem is availability and cost. Most hardware stores don't stock it, and when you find it online, a 40-pound bag runs $15 to $20. Unless your softener manual specifically calls for it or you have a very particular situation, the extra purity doesn't justify the price. Solar salt handles nearly all homes well enough.

What to avoid: table salt and anything with additives

Never put table salt, kosher salt, or sea salt in your softener. Table salt contains iodine and anti-caking agents that will clog your brine tank and corrode the softener's internal parts. Kosher salt has larger crystals and additives. Sea salt often contains trace minerals that don't dissolve.

Also avoid any salt labeled "with anti-caking agent" or "with iodine". These additives are safe to eat but will damage your softener. Stick to salt sold specifically for water softening — the bag will say "water softener salt" or "brine salt" on the label.

Pellets versus crystals versus blocks

Water softener salt comes in three physical forms. Pellets are small, uniform pieces about the size of a pea. They're the easiest to handle, pour smoothly into the brine tank, and dissolve evenly. Most people buy pellets.

Crystals are larger, irregular chunks. They're cheaper than pellets but harder to pour and can bridge — meaning they stack up and leave air gaps in the tank, so the softener can't access all the salt. Blocks are compressed salt in a solid form. They're convenient for storage but dissolve slowly and are prone to bridging. Unless your softener manual specifies blocks, buy pellets.

How to choose based on your water hardness and climate

If your water hardness is mild (under 10 grains per gallon) and you live in a warm climate, rock salt is fine. You'll save money and won't need to refill as often as someone with harder water.

If your water hardness is moderate to high (10 to 20 grains per gallon) or you live somewhere cold, solar salt is the better choice. The cleaner dissolution and better cold-weather performance will save you maintenance headaches. If your water is very hard (over 20 grains per gallon), solar salt is almost essential — rock salt will require frequent tank cleaning and may not regenerate efficiently.

Check your water hardness by looking at your most recent water report from your city or county, or by buying a test kit at a hardware store for $10 to $15. The number will be in grains per gallon or parts per million (ppm). One grain per gallon equals about 17 ppm.

Storage and handling tips

Keep salt bags in a dry place. Moisture will cause pellets to clump, especially rock salt. A basement, garage, or shed works well as long as water doesn't pool there. Don't store salt directly on concrete — put it on a pallet or shelf. Concrete can absorb moisture and cause the bags to stick.

When you refill the brine tank, pour the salt slowly to avoid splashing and damaging the tank's interior. Fill it until the salt level is about three-quarters of the way up. Don't overfill — the tank needs room for water during regeneration. Most softeners need refilling every four to eight weeks, depending on water hardness and household size.

Frequently Asked Questions

Can I switch from rock salt to solar salt or vice versa?

Yes. You don't need to drain the tank or do anything special. Just stop adding rock salt and start adding solar salt on your next refill. The softener will work with either type. If you're switching from rock salt to solar salt, you may want to clean out the brine tank first to remove any sediment buildup, but it's not required.

Why is my softener using more salt than it used to?

Your water hardness may have increased, or sediment buildup in the brine tank is blocking the brine line. If you've been using rock salt for years, clean the tank. If the problem started recently and you're using solar salt, your water supply may have changed — ask your water company for a new hardness test.

Does it matter what brand of salt I buy?

No. As long as the bag says "water softener salt" and contains no additives, any brand works the same. Store brands are identical to name brands and cost less. Buy whatever is cheapest and most convenient to find.

Can I use pool salt in my water softener?

Pool salt is usually rock salt or solar salt with no additives, so technically yes — but it's often sold in larger bags and may cost more per pound. Stick to salt labeled for water softeners, which is packaged in convenient 40-pound sizes.

What happens if I run out of salt?

Your softener will stop regenerating and stop softening water. You'll notice hard water symptoms — soap won't lather, dishes will spot, and your skin may feel sticky. Add salt as soon as you can. You don't need to reset anything; the softener will resume normal operation on the next regeneration cycle.