Does a bottle have to be made with boiling water?

I was just curious if formula milk has to be made with fresh boiled water, or is pre-boiled warm-hot water ok (say like the temperature as if it was kept in a flask)? Im wondering as when i was a nanny, the children's parents use to make the baby's bottle with 1/4 fresh boiled water and 3/4 room temperature distilled water because it would make the bottle the perfect temperature for the baby to drink straight away without having to wait for it to cool. Im due with my own baby any day now, and im not sure if this method is ok to use or should i just stick to using boiled water, and wait for it to cool? I know i could use a bottle warmer, but then the bottle would be made from cold water, no?