Combine the frozen berries, water, sugar and lemon juice in a medium saucepan over medium heat. Bring to a boil then reduce the heat to a simmer and cook until the berries have burst, about 6-9 minutes.
Remove from heat, add in the thyme leaves and let the mixture cool. Strain through a fine-mesh sieve without pressing on the berries – this won’t effect the flavor but will make the syrup cloudy. Save the sweetened macerated berries for topping on pancakes, smoothies etc.
Refrigerate the syrup until chilled. Keeps well for up to a week.
For the Lemon Thyme Sugar:
Combine the sugar, lemon zest and thyme leaves on a small plate or shallow bowl.
To Assemble Each Berry Spritzer:
Rim your glass with the lemon thyme sugar by first rubbing the rim with a lemon wedge or dipping in water, and then dipping and turning in the lemon thyme sugar.
Add 2 tablespoons of the berry simple syrup and 1 tablespoon of lemon juice to the glass.
Add in ice cubes or frozen berries, and top with 1/2 cup of sparking water. Stir gently. Enjoy!