How can we differentiate between glazed ceramic tiles that are waterproof and non-waterproof?    1) First, take a piece of dry ceramic tile and wipe both the front and back surfaces clean.    2) Then, take a cup of water or red ink and pour it onto the back surface of the tile. Pour it slowly, making sure not to cover the whole back of tile to facilitate clear observation.    3) Allow the tile to absorb the water for a while,    4) and finally, turn back the tile and check for any watermark. If there is a watermark, it means that the tile is non-waterproof. If there is no watermark, it means that the tile is waterproof.    Please check the following video, that will be more easy to understand. This kind interior wall tiles are used for bathroom and kitchen. If can accept price, we will suggest you to take waterproof finish.    How do you separate them? Any ideas, please contact us. Thank you!