In a medium saucepan, bring water to a boil over high heat. Stir in the curry paste, lime leaves and lemongrass. Bring to a boil again and add shrimps and mushrooms. Cook just until the shrimps are done but not overcooked. Stir in fish sauce and remove from heat. Spoon the soup into a serving bowl and add lime juice, stir to mix well. Sprinkle chilies and cilantro leaves before serving. Serve hot with cooked rice. Makes 2 servings. NOTE: Boneless chicken pieces may be used instead of shrimps. Omit the chilies if desired. Additional fish sauce may also be added to the soup at the table.