Hi! This is my first answer here 
My company deals with water treatment. The easiest solution (at an reasonable price) is to use an Everpure filter. There are 2 models which contain resin and activated carbon. So you can use tap water and treat it with a single filter (you only need head and fittings). What you get is a decrease of scale and the removal of chlorine (which make coffee more bitter). If you’re interested I can tell you more.
Best regards,
Hans