I see where you are coming from, but in reality tap is adding stuff to the water without a doubt. You are not adding cleaner water than is in the tank. get a tds
meter from ebay for under 10 bucks and then go from there if you dont believe me. lol
My tap has no nitrates, trace phosphates and reads 140tds. thats 140 of "stuff" that is in the water. I go through the ro
unit and it has zero nitrates, phosphates and more importantly, ZERO tds
. So therefore, I am adding higher quality water than I am removing.
I dont add any chemicals usually unless really needed and feeding will add things regardless of the water source. I know youre trying to angle this so tap is ok, if thats all you can do fine, I understand, but in reality it is not as clean as you think.
The water company adds all sorts of stuff to tap water, chemicals and flouride and other stuff.
If you are on well water then you risk heavy metals and other organic things.