Those that don't drink from your RV fresh water tank BUT wash dishes, SHOWER, wash hands etc.......
You do realize that the human skin is the largest organ and does absorb 'things' from water be it showering, washing hands in that water.
And those dishes.washed/rinsed in that water will also provide a means of 'things' in that water source into your body.
Besides......if you fill it with water from home it's just a big ole bottled water jug.
Granted there are some taste differences in water from region to region but rarely did we found any 'regular municipal supplied' water source that was an issue.