Add the ginger, water, and agave syrup to a small saucepan and bring to a boil over medium-high heat.
Once boiling for a minute or two, reduce to a simmer for about 15 minutes.
Strain out the ginger and cool the syrup completely. Store in the fridge.
For the refresher:
Muddle a few sprigs of mint in the bottom of a glass to bring out their scent and flavor.
Add ice to the glass. Pour the chilled ginger simple syrup into the glass about 1/4 to 1/3 of the way, depending on your preference.
Fill to the top with lime-flavored sparkling water. Squeeze in the lime juice.
Stir and garnish with a sprig of mint.
Notes
Add vodka to turn this ginger refresher into a cocktail!
You can squeeze the lime by hand or use a citrus juicer to extract its juice. But if you don't own a citrus juicer, you can press the lime with tongs.
Pour the ginger simple syrup into a bottle and seal. You can store the syrup in the fridge for up to 2 weeks or freeze it in ice cube trays for longer storage.