In a saucepan boil water, sugar and guavas until all sugar is dissolved. Reduce heat and simmer until guavas are tender, about 8 minutes. Remove from heat; cool completely. Once guava syrup is cool, place in blender and blend until smooth, strain and refrigerate. To a cocktail shaker filled with ice add gin, lime juice and 4 tablespoons guava syrup. Shake well and pour over two glasses filled with ice. Top with chilled Perrier L’Orange and garnish with guava wedges and lime slices.