• Deionized water is easier on taps and dishes.Buena Vista Images/Digital Vision/Getty Images
  
  Water deionization systems remove positively and negatively charged particles, otherwise known as ions, from a water supply before sending it on to taps or appliances. The charges that mineral ions carry can attract them to components in a water system, where they build up in a process known as "scaling." The three basic types of deionizers replace these problematic ions with other particles that also carry a charge, but will not build up.
  
  

Water Softeners

• Water softeners perform the most common type of deionization treatment: removing the scale-causing calcium and magnesium that makes tap water "hard." To do this, they pass water through a tank containing an ion-exchange resin that has been soaked in a sodium chloride (salt) solution. This resin is typically in the form of polystyrene beads. These beads have a chemical affinity for calcium and magnesium, so when hard water is passed through the resin these ions bond to it, pushing the sodium chloride ions out of the way and into the water to replace them. Eventually, all the sodium chloride is passed into the water and the softener must be reloaded with a new bag of salt for the reaction to work again.
  
  

Cation and Anion Deionizers

• Cation deionization also uses synthetic resins similar to those in a water softener, but doesn't add a sodium chloride solution. Instead, the resins themselves exchange positively charged hydrogen ions (or cations) with the positively charged mineral cations such as sodium, magnesium and calcium. A second type of resin exchanges negatively charged oxygen ions (or anions) with anions in the water such as bicarbonate, sulfide and chloride. The hydrogen and oxygen released into the water in the replacement process then combine into H20 (water molecules), leaving the water pure. Since these systems exchange ions from the resins themselves, the resins must regularly be changed as their ions are used up.
  
  

Mixed-Bed and Two-Bed Deionizers

• Cation/Anion deionizers come in two basic types. In mixed-bed models, the cation and anion resins sit in the same water tank. By contrast, two-bed deionizers have separate tanks for the cation and anion-exchanging resins that the water flows through sequentially. Mixed-bed deionizers tend to produce higher quality water treatment, but have lower water capacity than two-bed models. In both cases, the resin must be changed at the right time. Partially used-up resins can add dangerous chemicals to the water or boost the level of salts that new resins reduce.