In blender, combine all ingredients, except mineral water, until smooth. Strain into pitcher, discarding solids, and refrigerate until cold, at least 1 hour. Divide among 6 ice-filled tumbler glasses and top with still mineral water or extra chilled green tea, if desired. Garnish with slices of cucumber, frozen green grapes, and mint leaves, if desired. To make this a cocktail, add a shot of tequila.