Have you ever wondered how home filtration systems can effectively remove excess minerals from the water?  The answer lies within the very core of the filter, with something called an ion exchange resin.  Sodium chloride is added to the container of resins within the filter.  As the water passes through the resins, the sodium chloride is replaced by the calcium, magnesium, and iron in the water.  The sodium is, then, deposited into the water.  This exchange process takes place until all of the sodium has been exchanged, and then the life of the filter is over. 
     The ion exchange resins are combined within the filter with activated carbon and manufactured inside a prepared plastic.  Together, they replace toxins in the water, such as lead, copper, and mercury. The activated carbon acts as a sponge to trap unwanted ions of pesticides and oils.  The carbon also reacts with certain minerals, such as chlorine, and produces chloride and hydrogen ions which taste all right and are harmless to drink. 
     With all of the "exchanging" and "trapping"  within the filter, you may wonder why home filters last as long as they do if they are removing millions of toxic ions from each gallon of water.    The answer can be found when analyzing the "pure" water.  The ion exchange resins and activated carbon do not leave "pure" water after filtration.  "Pure" water would have no ions, and therefore, no minerals.  This water would taste VERY funny.  Therefore, the filters are not actually removing all of the minerals that run through them.  They are, though, exchanging minerals.  Because an exchange of ions is taking place and only a certain percentage of minerals are being removed from the water, the filters are able to filter through a fairly large amount of water with less harmful ions and a acceptable taste.