I don't see what the big deal with just using hard water. our local water supply is hard due to percolation of rainwater through lava and then in a well in coral.
Waqter from the tap can produce white calcium deposit formations on pots, sometimes leaves and soil. I have grown all my neps in this condition with no ill effect. Your media is rather acid (if you use peat, LFS, coco chips, composts, leaf mold, etc.) so watering with hard water would somewhat neutralize the effect.

I have not seen any problems with watering with hard water. Has anyone had any effects due to hard water use?