When I first stopped breast feeding and moved onto formula feeding I made the bottles up as per instructions on the box. But as Thomas was so young when he wanted a bottle he wanted it immediately and would scream blue murder whilst I was trying to cool the boiling hot milk for him to drink. Spoke to a midwife about it and she said to ignore the instructions (she joked they must have been written by a man who had never had to deal with a screaming baby at 3 in the morning!!). She said to sterilise the bottles, boil the water and let it cool in the kettle for 30 minutes. Put the cooled water in the bottles and put them in the fridge, this keeps everything sterile. Then when you need to do a feed get the bottle out of the fridge, add the milk powder and then warm the bottle in a bowl of hot water. I actually only part fill the bottle with cool water before putting it in the fridge, then top it up with boiling water at feed time so it's the right temp - again everything is sterile as water has been in the fridge and the added water is boiled. We haven't had any upset stomachs in the 9 months I've been doing this!!