Pour salt on a small plate. Run a lime wedge around the rim of an 8-ounce glass and dip in salt. Fill the glass with ice.
In a cocktail shaker or cup, add lime juice, orange juice, lemon juice, and agave nectar. Shake or stir to combine.
Pour into prepared glass, top with sparkling water, and garnish with a lime wedge.
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Notes
Agave nectar: If you don't have agave nectar, you can use simple syrup or honey instead.
To make ahead: Stir all of the juices together with the agave and store in a sealed jar or airtight container in the fridge up to 1 day ahead of time. When it’s time to serve, give the mix one final stir and top each glass with sparkling water.
To make a big batch: You can double or triple this recipe if you’re serving a crowd. Just stir the batch together in a pitcher and don’t add the sparkling water until right before you serve the mocktails. Leave a plate of salt and lime wedges out in case your guests prefer to salt their rim.