In a small sauce pot combine the sugar and water. Cook on medium for 5-7 minutes or until the sugar is fully dissolved. Remove from heat and let cool.
In a large pitcher combine the cooled simple syrup, lime juice, guava nectar, tequila and lime slices. Stir to combine and refrigerate until needed.
To serve, dip glasses in lime juice and then salt. Pour the guava margaritas in the glasses and serve.
Recipe Adapted from The Foodie Bride.