The condition of your water is vital to espresso quality and the longevity of your espresso equipment.  There are three basic types of water filtration/conditioning commonly used, the following information will help you understand the diferences between various systems.

 Filtered water: 
      Usually a carbon based filter medium, filters will remove particulate matter down to a specified micron rating (ex. .5 micron).  Filtered water will generally remove harmful bacterias, cysts, as well as chlorine and other undesireable tastes, odors, and turbidity.  However filtered water alone does nothing to help prevent mineral scale buildup in your equipment.

Softened water: 
      A water softener actually removes the minerals that can build-up inside of your equipment.  This is accomplished via an ion exchange within the softening "grains" in the cartridge.  A softener has no effect of other aspects of your water quality.  Many people think they have "good" water, but taste or clarity is no indication of the mineral content of your water. Water reports containing this information are available from your local water district office.  The effective life of the cartridge is a direct relation between the PPM "hardness" of your water and the total grains in the softener cartridge.  This can be determined with the following equations PPM/17.1=GPG (grains of hardness per gallon),  total cartridge grains/GPG=Total treated gallons.
      An example would be, water hardness of 45 PPM and an 1100 grain softening cartridge; 45/17.1=2.6GPG, 1100/2.6GPG=423 gallons of treated water.  Once the effective lifespan of a cartrdge has been exceeded, there is NO benefit or protection to your equipment.

Two-stage Combination systems: 
      Combining the carbon based water filter AND a softening cartridge offers the best of both worlds providing the improved taste of filtered water with the protection to your equipment from the softener cartridge.