Looks like hard water to me... is there any powder on the soil?

Yes Hard water collecting some rain water/snow melt. Good luck.

no there is no powder on the soil. I have been using my local tap water. is hard water detrimental or dangerous to my plants health?

Not really, and water softened by osmosis has salt, which is very bad for trees.

Reverse osmosis water filter systems that are working properly produce water with 0 PPM dissolved solids - so pretty much the equivalent of distilled water. I use R/O for all my plants over-wintering under lights (to eliminate build-up EC/TDS in the soil solution). Some deionizing systems replace the magnesium, calcium, and sometimes iron, in your water with sodium or potassium ions. Those systems represent unacceptable sources of irrigation water (if you ask your plants).

Has the 'powdery residue' appeared while the plant was in your care, or did you buy it that way?

BTW - boiling water doesn't remove dissolved solids from water. It would be counter-productive because as the water evaporates, it leaves ALL the dissolved solids behind, so it actually concentrates the level of stuff dissolved in your water. Most tapwater has the potential to be a problem for plants because of what it contains. Carbonates, fluorine, chloramine are all potential limitations, but how severely limiting they become depends a LOT on your soil choice and watering habits. If you're flushing the soil when you water, they are much less likely to be severely limiting than if you're watering in small sips so the soil doesn't get/stay soggy for extended periods - another serious issue unto its own.

Al