If you have a lot of plants together (this is the way it appears) the leaves will overlap and water can hide in certain spots......especially in higher humidity like yours.
Wobster mentioned splashing and I think its' along the same line so you have two votes for lightburn.

Without knowing what kind of nutes you use I would suggest two changes but I'm not sure either of these is YOUR issue.......at the moment. I would stop using botttled drinking water and go with either distilled or RO and CalMag or use the water from your tap unless its too hard. Bottled water carries its own issues.....including higher sodium content I believe among other issues.

Dropping the humidity in your room may also help.....70% is pretty up there (I like mine in the 30's) so that is something to think about for future........especially in flower where mold and fungus will throw a HUGE party on your plants with the higher humidity.