It is common knowledge that soft water, either naturally occurring or from a water softener, has greater cleaning power than hard water.  If you have ever taken a shower in soft water you know that a little bit of soap goes a long way.  The same is true when washing clothes in the washing machine or even washing dishes in the sink; it takes about half the amount of soap as it does in hard water to produce a nice rich lather.  But why is this?  Why are soaps and detergents more effective in soft water than in hard water?
To answer this question, let’s first look at the chemical make-up of hard water.  Hard water, by definition, is water which contains a high concentration of calcium and magnesium ions; it is these minerals which prevents soap and detergents from being as effective as they should be.  When the “soap” molecules come in contact with the magnesium and calcium in hard water, a chemical reaction occurs and magnesium stearate or calcium stearate forms; this is the waxy substance we all know as soap scum.  This reaction prevents the soap from producing the cleansing lather as it was intended.
It is a completely different story for soft water.  Naturally occurring soft water does not have these minerals present and therefore detergents and soaps do not react as they do in hard water.  Water that has been softened by a water softener, typically replaces the magnesium and calcium minerals with sodium or potassium; these minerals do not react with the compounds in soap or detergents so they perform as they were intended.
Not only does soft water require much less detergent than hard water to be effective, there is another cost savings benefit associated with soft water as well.  Due to the fact that detergents clean more efficiently in soft water, washing machines do not have to be set on hot in order to achieve good stain removal.  Cold water washes accomplish the same or even better stain removal, and produce whiter whites than clothes washed in hard water.  So not only do you see a 50 percent reduction in detergent needed, homeowners can also save energy by not having to use hot water.