In a medium saucepan, combine the water, honey, thyme, and ginger. Bring the mixture to a boil over medium-high heat, then reduce the heat and let it simmer gently for 5 minutes to infuse the flavors.
Once done simmering, remove the pan from heat and stir in the lemon zest and lemon juice. Cover the pan and allow the mixture to steep for 20 minutes so the herbal and citrus notes fully develop.
Strain the liquid through a fine-mesh sieve into a medium-sized bowl, pressing lightly to extract every drop of the infused syrup. Discard the solids and transfer the mixture to the refrigerator to chill completely—at least 2 hours or up to 5 days in advance.
When ready to serve, pour ¼ cup of the chilled lemon-thyme concentrate into a glass. Add ½ cup of sparkling or still water, and stir. For a spirited twist, include 1 ounce of gin or vodka. Garnish with a fresh thyme sprig and serve immediately.