Bring 2 cups of water to a boil in a kettle.
Pour the boiling water into a heatproof pitcher or teapot.
Add 2 tablespoons of dried hibiscus flowers to the hot water and stir gently.
Steep for 5 to 10 minutes, depending on how strong you like it.
Strain the tea through a fine-mesh strainer into a clean pitcher or heatproof bowl, discarding the flowers.
If desired, stir in 1 to 2 tablespoons of granulated sugar until dissolved.
Serve warm right away, or let the tea cool to room temperature, then refrigerate until chilled.
To serve cold, pour the tea over ice and garnish with a lemon slice.
Optional: add fresh mint leaves while steeping, or serve with berries or orange slices for extra flavor.
Store any leftover tea in a sealed pitcher in the refrigerator for up to 3 days.