Cut well-washed rhubarb into 1cm (half-inch) chunks. Place in a glass or ceramic bowl. Cover with boiling water.
Allow to steep at room temperature for about 12 hours.
Pour off juice; discard rhubarb pulp.
Sweeten juice to taste with sugar or other sweetner (agave, honey, etc). Flavor and garnish with lemon or lime. Dilute with carbonated water or soda, if desired. Serve with lots of ice.