Add the seedless watermelon cubes to a blender and blend on high for 30–45 seconds until completely smooth and liquid, with a visibly uniform pink mixture.

Pour the blended watermelon through a fine mesh strainer or cheesecloth over a large pitcher, pressing gently with a spoon to extract as much liquid as possible, until the pulp is mostly left behind and the liquid runs clear.

Discard the pulp and transfer the strained watermelon juice back to the pitcher, leaving a smooth, seedless base.

Stir the cold water, fresh lime juice, sugar or honey, and a pinch of salt into the strained watermelon juice until the sweetener fully dissolves, with no visible sugar grains.

Taste and adjust by adding more lime for brightness, more sweetener if the watermelon isn’t very ripe, or more water to thin, aiming for a balanced sweet-tart flavor.

Add the fresh mint leaves directly to the pitcher and stir gently, then let the mint steep for at least 5 minutes (or refrigerate for up to 30 minutes for a stronger mint note) for maximum flavor.

Fill tall glasses with ice, then pour the agua fresca over the top, keeping the surface cold and frosty.

Garnish each glass with a sprig of fresh mint and a lime wheel, then serve immediately for best aroma.