There are a lot of questions intertwined in "How do we fix water?" What are the variables?
First, the water itself:
1. Is it only TDS that affects taste? Does mineral composition matter?
2. How can we measure this in a home or commercial setting?
3. Assuming TDS is the main driver, is it simply a matter of reducing TDS, or is there a range best suited for different brewing methods? (Higher for press, medium pour over, low espresso?)
Secondly, what is state of the art?
4. What are the options to solve this problem? Reverse osmosis, charcoal filters, water softeners, bottled waters, spring/natural source waters? How do these affect the water, and to what extent?