I wouldn't use tap water at all if I can help it. I know that mine comes into my house @ 120 ppm
Which by water quality goes is pretty good most ive heard are well above 300. my rodi
puts out water @ 0 Top ups and water changes should be done with rodi
water. Then you can be sure your not adding chemicals like fluoride, chlorine, lead . Ect ect and whatever other chemicals you could imagine are in tap water. If you happen to have a well at your house I wouldn't even think about it. I would guess its upwards of 1500 ppm
of things such as iron, sulfur, phosphate. Definatly things you don't want in your system.
If you ever do happen to use tap water use prime from seachem. It removes chlorine and chloramine and ammonia and detoxifies nitrate & nitrite so the water becomes more " fish safe"