Peel 15 tamarind pods, discarding the shells and fibrous strings.
Measure 12 cups of water. Bring half of it to a boil in a large pot, add the tamarind, cover, and cook over medium heat for 8 minutes. Let cool completely.
Squeeze the seeds out by hand and discard them. Blend the pulp and cooking liquid until smooth and strain into a pitcher.
Stir in the remaining water and 1 cup of sugar, sweeten to taste, and serve over ice.
