Add hibiscus and water to a medium saucepan and place over medium-high heat. Bring to a boil, then reduce to a simmer for 15 minutes. Remove from heat.
Strain the hot liquid through a fine-mesh sieve to remove the flowers and any solids. Measure the remaining liquid, then return it to the pot over medium heat. Measure out the same amount of sugar as the liquid. Stir until completely dissolved.
Remove from heat and let cool completely.
Store in a clean, food-safe, airtight container such as a mason jar in the refrigerate for up to 1 month.