First, prepare your fresh ingredients. Juice the lemon and the grapefruit into separate glasses or a small bowl. You'll want about 30-45 ml of lemon juice and 100-150 ml of grapefruit juice, depending on the size of your fruit.

Take your fresh thyme sprigs. Gently crush them a little bit with your fingers or the back of a spoon. This helps release their aromatic oils and distinct flavor.

In a serving glass, combine the fresh lemon juice and grapefruit juice. Add the lightly crushed thyme sprigs to the glass.

Fill the glass generously with ice. The more ice, the colder and more refreshing your mocktail will be!

Top off the mixture with sparkling water. Stir gently to combine all the flavors without losing too much fizz.

For a lovely presentation, decorate your mocktail with a fresh lemon slice or a few extra thyme leaves.

Serve immediately and enjoy your wonderfully refreshing drink!