Combine half a cup of white sugar and half a cup of water in a small saucepan. Heat over medium-low heat, stirring gently until the sugar fully dissolves, about 3-5 minutes.

Allow the syrup to simmer until it reduces by half, then remove from heat and let it cool completely.

Cut about one seedless watermelon into cubes and blend until smooth for about 1-2 minutes. Strain the puree through a fine-mesh strainer into a large bowl or pitcher.

In a large pitcher, pour in the strained watermelon juice. Add the cooled simple syrup and approximately half a cup of freshly squeezed lemon juice. Stir well for about 30 seconds.

Taste the lemonade and adjust sweetness or tartness as needed.

To serve, fill tall glasses with ice, pour the watermelon lemonade over, and garnish with a wedge of watermelon or a slice of lemon.