1/2 cup chopped lemongrass stalks (use bottom 6-8 inches)
1/2 cup sugar
8 cups water
Bring lemongrass pieces, sugar, and 2 cups water to a boil in a 2-quart heavy saucepan, stirring until sugar is dissolved, then remove from heat and let steep, partially covered, 20 minutes.
Put remaining 6 cups water in a pitcher. Blend lemongrass mixture in a blender until lemongrass is finely chopped (use caution when blending hot liquids), then pour through a fine-mesh sieve into water in pitcher, discarding solids. Serve over ice.
Lemongrass tea can be made 1 day ahead and chilled, covered.
This modified recipe is from Epicurious.