i am not an expert in this, but i had the same query when i first started to bottle feed breastmilk to my baby. i was told that the water left in the bottles AFTER the sterilisation is "sterilised water" anyways so just shake it out just before you want it used. so i take my bottles out, re-assemble them and then put them in a sealed box in my fridge. then i just shake out any excess water when i am about to fill them with some thawed milk