Place the dried hibiscus flowers in a fine-mesh strainer and rinse under cold water; drain well.
Combine the water and granulated sugar in a nonreactive saucepan. Bring to a boil over medium-high heat, stirring until the sugar dissolves, 3–5 minutes.
Stir in the flowers, reduce to a gentle simmer, and cook 5 minutes.
Remove from heat, cover, and steep 10–15 minutes, until the liquid is deep ruby and the flavor is bright-tart with a rounded sweetness.
Strain through a fine-mesh sieve into a heatproof pitcher; discard the solids.
For hot hibiscus tea, serve right away.
For iced hibiscus tea, let cool to room temperature, then refrigerate until cold, about 1 hour.
Serve over ice cubes and with lime wedges for squeezing.