In a medium saucepan, combine 2 cups of the water and the sugar. Bring to a boil; remove from heat.Advertisement
Stir in lemon juice and 8 sliced radishes. Let stand, uncovered, 20 minutes.
Stir in remaining 3 cups water.
Remove radishes with a slotted spoon. Serve over ice with fresh cucumber and radish slices, or a whole radish.