This is a difficult topic, and there is no one single universal answer. The best I can offer is guidance, here are the three main scenarios:
Hard water:
Soften with reverse osmosis (effective but expensive)
Soften with ion exchange eg.a Brita (not as effective, cheap)
Bottled mineral water (wasteful)
Recipe water - homemade or Third Wave Water (extra work, relatively expensive if demineralised water is not cheap to acquire)
Soft to Medium Hard water
Soften with ion exchange eg.a Brita (not as effective, cheap)
Bottled mineral water (wasteful)
Recipe water - homemade or Third Wave Water (extra work, relatively expensive if demineralised water is not cheap to acquire)
Do nothing, if the water isn’t too bad. (The best option of all, but only useful to those whose water is in the range around ideal)
Soft Water
Remineralise your water (cheap, but extra work)
Bottled water (wasteful)
If you want to read more about water:
Water for Coffee (out of print for now, hard to get hold of - but excellent)
https://baristahustle.com/blog/diy-water-recipes-the-world-in-two-bottles/