Whisk egg white with water in a small bowl. Working with 1 flower at a time and holding it with tweezers, brush egg wash over entire surface of flower using a small paintbrush. Sprinkle with sugar. Transfer to a baking sheet lined with parchment to crisp flowers. Let stand at room temperature overnight. Sugared flowers can be stored in single layers in airtight containers at room temperature for up to 3 months.