When you make up your babies bottles in bulk, just pour the measured water into the bottle and put it in the fridge then as and when you need them, heat the water then add the formula. That way, if the formula doesn't get used you can heat it 1 more time, where as if you make them up complete you can only reheat the formula and then throw away. Also, if it isnt used in the time space they get thrown and formula wasted.