https://en.wikipedia.org/wiki/Dishwasher_salt https://en.wikipedia.org/wiki/Dishwasher_salt The water hardness setting determines how much the water softener t

https://en.wikipedia.org/wiki/Dishwasher_salt https://en.wikipedia.org/wiki/Dishwasher_salt The water hardness setting determines how much the water softener tries to soften the water. If the water isn't soft enough, it will leave spots on the dishes. Hence people use "rinse aid", so the improperly softened water would drip off before it leaves spots. If the water is properly softened it contains no calcium etc. which could cause spots on your dishes.