Water treatment is preventative maintenance! Garbage in, garbage out! The water not only needs to be treated to protect an espresso machine from damaging limescale deposits, but to also extract more desirable flavor profiles.
Reverse osmosis and distilled water are also not good for two reasons: first, they can be corrosive with the metal inside an espresso machine and cause oxidation in certain instances; and, second, these two water types do not have enough minerals to extract the oils from the grind, leaving a flat tasting flavor profile.
Water softening is different than filtering water. Water filters remove bad taste and odors, chlorine, and sediment. If the filter does not have a limescale inhibitor built in, the water should be softened with a softener.
If you are unsure what you need, please inquire using the Contact Us link at the top of this page. To learn more, please choose the link based on your current set up: Direct Plumbing or Reservoir