Preparing formula???

Lu

So ladies I have a formula question, I just switched my five month old to formula and since it’s so hot, have been boiling a litre of water and then I put it in a glass container to use throughout the day to prepare bottles. Is this wrong?? Does the water once cooled all the way expire and can no longer be used to prepare a bottle??? My daughter hasn’t had any ill effects by me doing it this way, was just wondering if I have to re boil the boiled water. Thanks