Combine first 4 ingredients in top of double boiler. Bring water to a boil; reduce heat to low and cook till chocolate melts, stir constantly. Add butter, one piece at a time, stir with wire whisk till butter melts and mixture is smooth. Remove from heat, and stir in gingersnap crumbs. Cover and chill 8 hours. shape mixture into 1" balls. Roll balls in nuts or sugar. place truffles in candy paper cups. Store in airtight container in fridge.