In a saucepan over medium heat, combine strawberries, basil leaves, sugar, and water. Stir occasionally, heating for about 5–10 minutes until the sugar dissolves and strawberries soften.

Remove from heat and strain the syrup through a fine-mesh sieve into a bowl, pressing down to extract liquid. Discard solids and let cool.

In a tall glass, combine the strained strawberry basil syrup with lime juice. Stir well to blend.

Fill the glass with ice cubes and top with club soda. Stir gently.

Garnish with a fresh strawberry slice or basil sprig and serve immediately.