Add the 500g of cubed watermelon flesh, 30ml of fresh lime juice, zest of ¼ lime, and 20g of honey to a blender. Blend at high speed for 45–60 seconds until completely smooth and liquid — no visible watermelon pieces remaining. Watermelon's flesh is primarily water and dissolves rapidly into a smooth liquid at high speed. Place a fine-mesh sieve over a clean jug or bowl. Pour the blended watermelon through the sieve and press gently on the pulp with the back of a spoon, extracting as much juice as possible while the remaining dry pulp and any stray seeds stay behind. The straining step is what separates this mocktail from a simple watermelon smoothie: strained watermelon juice is visually clear-bright and brilliant pink, mixes cleanly with the club soda without producing foam or floating pulp particles, and feels specifically lighter and more refreshing in the glass than the thicker, slightly muted texture of unstrained blended watermelon. Press until the pulp in the sieve is relatively dry, then discard it.

Take the 16 fresh mint leaves and hold them in one hand with the leaves stacked flat. Clap your palms together firmly over the watermelon base once or twice — the sharp impact compresses the mint leaves momentarily and ruptures just enough surface cells to release the aromatic oils from the leaves' surface without the deeper bruising that muddling or tearing causes. A clapped mint leaf releases its aromatics as surface volatile compounds — specifically the fresh, cool, clean menthol-adjacent character that makes mint immediately refreshing. A torn or heavily muddled mint leaf releases more of the chlorophyll and deeper cell contents alongside the aromatics — contributing the grassy, slightly bitter undertone that is the difference between mint as a refreshing aromatic and mint as a herb flavour. Add the clapped mint leaves directly to the strained watermelon base in the jug. Cover and refrigerate for 30 minutes. The cold infusion is the specific technique that makes the mint's contribution specifically fresh and clean in this mocktail. At cold temperature, only the most volatile surface aromatic compounds transfer into the surrounding liquid during the 30-minute window — producing the cool, fragrant, fresh mint character that a few seconds in hot liquid cannot replicate. Warm steeping would extract the mint's full aromatic range including the less pleasant, more medicinal back notes; cold infusion for 30 minutes extracts only the pleasant, forward volatile freshness. After 30 minutes, remove and discard the mint leaves.

Fill four tall glasses generously with ice cubes. Divide the chilled watermelon-mint base evenly among the four glasses — approximately 125ml per glass, or roughly filling each glass to just above halfway. Top each glass with approximately 125ml of chilled club soda — the 1:1 ratio producing a drink that is vivid in watermelon colour and flavour while the equal volume of carbonated water provides the specific lightness and effervescence that makes the fizz format work. A ratio with less watermelon base produces a pale, mildly flavoured fizz; more watermelon base produces a denser, less effervescent result closer to still watermelon juice with bubbles. The 1:1 is the specific balance. Pour the club soda gently down the inner side of each glass to preserve the carbonation. Stir once or twice only — enough to distribute the watermelon base through the club soda without fully blending them, maintaining the slight colour gradient as the two liquids meet. Place a small watermelon wedge on the rim of each glass by making a small cut into the base of the wedge. Rest a fresh mint sprig in the ice with the leaves above the rim. Serve immediately.