If my tap wasn't so horrid I would just use it. After struggling for months to get my parameters stable I chose to go with RO water. My water is not only bad but unstable. I would rather do the same thing every week for my big change instead of having to track weather conditions fertilizers farmers are using. I live in farm country and do have city water. But these are the varying conditions of my tap water I also don't drink my water anymore either.
Ammo 0-2ppm
Nitrite 0-1ppm
Nitrate 0-40ppm
PH - 7.2-8.8
Phosphate .5-2ppm
I don't have tuns of records on gh and kh
GH 25-35 447-572ppm
KH 13-15 232- 268ppm