I make up bottles in advance. I boil the kettle and let it cool n make up all the bottles with just the wster n put them all in the fridge. I make up enough for about 12hrs so i do it twice a day. I then take out a bottle as i need it n add the formula n then warm it. Oliver gets hungry very suddenlt n just screams so making up a bottle 100% fresh every time wouldnt suit us.