Heat the lime juice, agave nectar and ginger in a small saucepan. Bring mixture to a full boil, then reduce heat to a simmer and cook 5 minutes. Strain the ginger using a fine mesh strainer. Use the back of a spoon to press the ginger against the strainer to get all of the juice out. Allow simple syrup to cool.

Rim four glasses with coarse sea salt by wetting the rim with lime juice or water and dipping in salt.

Prepare the margaritas in a large batch by stirring together the ginger-lime simple syrup, tequila, and sparkling water in a pitcher. Fill four glasses with ice and divide the margarita between the glasses. As an alternative, you can prepare the margaritas one at a time by adding 2 tablespoons of simple syrup, 2 ounces of tequila, and ¼ cup of sparkling water to each ice-filled glass. Stir well and serve with wedges of lime and enjoy!