Making formula with boiled and bottled water??

My baby is 6 months old and for the first few months (while we mixed formula/breastmilk) we made the formula with boiled tap water as instructed. Then we started exclusively formula feeding at 4 months and it took a long time for the formula to cool down so I started topping the bottle off with a little cold bottled water. Probably 80% boiled sterilised water and 20% bottled water.

I just read that bottled water isn’t good for babies and am now worried I’ve messed up my baby. Does anyone have advice??