If you have a salt-based water softener, you'll be buying salt regularly. The four main options vary in purity, price, and performance - and using the wrong type can cause problems.
Rock salt
The cheapest option ($4–6 per 40-lb bag). Rock salt is mined directly and contains more insoluble impurities (1–5%) than other types. These impurities accumulate in the brine tank as sludge, requiring more frequent tank cleaning. Best for: budget-conscious households willing to do more maintenance. Avoid if you have a higher-end softener - the impurities can clog valves.
Solar salt
Made by evaporating seawater or brine in solar ponds ($5–8 per 40-lb bag). Higher purity than rock salt (99.5%+) with much less residue. Comes in crystal or pellet form - pellets are easier to handle and less likely to bridge (form a hard crust in the tank). Best for: most households. Good balance of price and performance.
Evaporated salt
The highest purity ($6–10 per 40-lb bag). Produced by mining underground salt deposits and evaporating the brine. Purity of 99.9%+. Almost no residue, minimal tank cleaning needed. Best for: high-efficiency softeners, households that want minimal maintenance, and areas with very hard water where the softener works harder.
Potassium chloride
Not technically salt - uses potassium instead of sodium ($20–30 per 40-lb bag). Same ion exchange process, but replaces hardness minerals with potassium instead of sodium. Pros: no sodium added to water, better for sodium-restricted diets, more environmentally friendly discharge. Cons: significantly more expensive, slightly less efficient (may need to increase settings by 10%), and harder to find in some areas.
Tips for using softener salt
Keep the tank at least 1/4 full but don't overfill - leaving space above the salt prevents bridging. If you see a hard salt crust forming (salt bridge), break it up with a broom handle. Don't mix salt types in the same tank - use one type consistently. If switching types, let the tank run low first.
Check your water softener guide for more on maintenance and sizing.