Chop the watermelon into 1 inch cubes, removing the peel and the big seeds.
Juice the lemons.
Add the watermelon cubes, the lemon juice, and the honey or simple syrup to a blender and blend until smooth.
Strain the mixture into a bowl or very large pitcher through a fine mesh strainer. You will end up with about 4 cups watermelon lemonade concentrate.
To serve, add the watermelon lemonade concentrate and an equal amount of cold water to a pitcher along with some ice. Alternatively you can add 1/2 cup of the concentrate to each cup, over ice, and top up with water or sparkling water.
Notes
Storage and Freezer Instructions
This watermelon lemonade concentrate keeps well in a jar or airtight container in the fridge for 3-5 days. You can freeze this watermelon lemonade concentrate in ice cube trays for up to 3 months and defrost it in sparkling water or in a serving pitcher.