Begin by cutting a ripe watermelon into chunks, ensuring it’s chilled. Blend the watermelon chunks until smooth (1-2 minutes), then strain through a fine sieve to extract juice.

In a medium saucepan, combine the watermelon juice and sugar. Bring to a gentle simmer (3-5 minutes) until the sugar dissolves. Cool the mixture in a pitcher in the refrigerator.

Squeeze fresh lemons to obtain about a cup of lemon juice. Set aside for later use.

In a large jar, layer thin lemon slices at the bottom, add pebble ice, filling about a third of the way.

Pour in the cooled sweetened watermelon juice, followed by the fresh lemon juice and sparkling water, maintaining a 2:1 ratio of watermelon to lemon juice.