Can buy citric acid from most supermarkets. Usually in the baking sections. Just mix a little bit with water and cover the metal part then use sponge to wipe off. After that rinse with water can already.Hi, anyone out there know where to buy citric acid?? I need it to descale the sterilizer (avent). When I bought the sterilizer they attached two packets in it. Indicated that is adviseable to descale every 4 wks. Any idea where to purchase it??