they're intended to "remove" calcium and magnesium salt ions by exchanging them with sodium ions from the ion exchange resin beads in the filter, thereby softening the water (and to most people making it taste better)

however ion exchange uses osmosis to function. you can "recharge" an ion exchange resin by putting it in a brine with a super high sodium concentration, causing the exchange to run in reverse (the sodium ions will replace the calcium and magnesium in the resin instead of the other way 'round).

so in this photo, the filter is removing salt the opposite way it normally does lol