Rinse the dried chrysanthemum flowers to remove any excess debris.
Bring the water to a gentle boil, remove from the heat, and then add the chrysanthemum flowers. Allow the flowers to steep in the water until the drink is bright yellow in color, anywhere from 10-30 minutes. This will result in a strong floral flavor. If you prefer a less pronounced flavor, steep for less time.
Pour the chrysanthemum drink through a strainer to remove the flowers. Add sugar and stir to dissolve while the drink is still warm. Start with 2 Tablespoons, and add more as necessary. This drink is also good without sugar, although those served in Thailand are typically quite sweet.
Chill the chrysanthemum drink for several hours. Once it is cold, pour into a glass filled with crushed ice, and enjoy.