Notes: If making up to 4 hours ahead, cover and chill puréed mixture; add ice just before serving.
Cut and discard pits and peel from mangoes. Cut fruit into chunks.
In a blender or food processor, in batches, whirl the mangoes, orange juice, mint leaves, and 5 cups water until smoothly puréed; pour into a pitcher. Stir in 1/4 cup lemon juice, or to taste.
Pour agua fresca into ice-filled glasses. Garnish with mint sprigs.
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