High quality water is an absolute must when brewing coffee. A poor quality water will affect the taste and aroma of coffee. It is best to use filtered water when brewing coffee. Tap water may contain unwanted chemicals (chlorine, iron, etc..) which will affect the taste of brewed coffee. Chemicals can also leave residue in your coffee maker.
Tests have shown that water that contains chlorine or other odors will affect the taste of brewed coffee. This is easily treated with a carbon water filter.