Very rarely minerals that naturally occur in hard water can leave a white residue on silicone products commonly spotted on wine glasses cleaned in the dishwasher. This residue is not harmful and shouldn’t alarm you.
A simple trick to keep your We Might Be Tiny products squeaky clean is to wipe them down rather than letting them drip-dry. And if you need to remove any existing residue, simply pop your We Might Be Tiny product in boiling water.