Place watermelon cubes, lime juice, mint leaves, cucumber and honey in a blender and mix until smooth.

Using a fine mesh strainer and a spatula, pour the watermelon puree through (into a bowl) and press down with the spatula to strain out any pulp. Discard pulp.

Pour watermelon puree into a pitcher. Stir in seltzer water when ready to serve. Stir or blend to mix. Alternately, you can pour into glasses, over ice, about half full and add seltzer water to each glass.

Serve over ice, garnished with watermelon cubes or slices and mint leaves, if desired.