A salt softener removes hardness by ion exchange: water passes through a bed of resin beads that hold sodium, the beads grab calcium and magnesium and release sodium in their place, and when the beads are full a brine rinse recharges them. The salt never touches your water directly; it only recharges the resin.
The exchange, in plain terms
The USGS defines hardness as dissolved calcium and magnesium, and those are exactly the two ions a salt softener targets. Resin beads in the tank carry a negative charge and hold loosely bound sodium ions. Calcium and magnesium have a stronger affinity for the resin, so as water flows through they stick and sodium is released. That continues until the bed runs out of exchange sites, at which point hardness starts appearing at the taps again. Nothing is filtered in the ordinary sense: the hardness is swapped, not strained, which is why a softener does nothing about sediment or chlorine.
What happens during regeneration
Regeneration is the cycle that recharges the bed, and it runs in stages. A backwash lifts and rinses the resin to clear trapped debris. Then concentrated brine drawn from the salt tank is pulled slowly through the bed, and the sheer concentration of sodium reverses the exchange, stripping the calcium and magnesium off the beads and flushing them to drain. A slow rinse follows to push the brine through, then a fast rinse settles the bed, and finally the brine tank refills with fresh water to dissolve more salt for next time. All of that needs a drain line and power.
Metered, timer and on demand controls
A timer valve regenerates on a fixed schedule regardless of how much water the house used, so it wastes salt in a quiet week and runs out of capacity in a busy one. A metered valve counts the actual water treated and regenerates when the calculated capacity is used, which is why it is the sensible default for most households. On demand and twin tank systems go further, either learning the household pattern or bringing a second resin tank online so soft water is available even during regeneration. Whichever you have, the settings depend on your measured hardness.
Salt types and the problems they cause
Softener salt comes as crystals, pellets and blocks, and as rock, solar or evaporated grades that differ in purity. Cleaner grades leave less insoluble residue in the brine tank. Two classic faults come from salt itself: bridging, where a crust forms over an empty space so the tank looks full while no brine is being made, and mushing, where fine salt recrystallizes into a sludge at the bottom that blocks the brine draw. Both present the same way, as water that has quietly gone hard again while the tank appears to have plenty of salt in it.
Keeping one working
Keep the salt level above the water in the brine tank and break up any crust you can feel with a broom handle. Clean the tank out occasionally, especially with lower grade salt. Check that the brine tank refills after a regeneration, since a blocked injector or a failed float is a common cause of a softener that runs but does nothing. Test a treated tap for hardness now and then rather than trusting the feel of the water. Our water softener installation guide covers where the unit belongs relative to filters and the water heater.
Questions people ask about salt softener
Does a salt softener make water taste salty?
No. The brine is rinsed to drain during regeneration, and what ends up in the water is a small amount of sodium exchanged for hardness minerals, which is not tasted at typical hardness levels.
What is the difference between softener salt and table salt?
Softener salt is sold in crystal, pellet and block form and is graded for purity so it dissolves cleanly. Table salt contains additives and fines that foul a brine tank.
Can a salt softener remove iron?
It can handle a limited amount of dissolved iron, but oxidized iron fouls the resin. Where iron is significant, fit a dedicated iron filter ahead of the softener.
How do I know my softener has stopped working?
Scale returning on fixtures, soap not lathering, and spotting on glassware are the practical signs. Confirm with a hardness test on a treated cold tap rather than by feel.