Cut watermelon into large pieces and discard the skin. Remove black seeds, no need to take the white seeds out.
Add watermelon pieces in a blender jar.
Blend until smooth texture.
Transfer it to a large bowl.
If watermelon is sweet, no need to add sugar, but if it is not, taste the juice and if required, add sugar.
Add lemon juice and fresh mint leaves if you like . Stir well.
Add 1-ice cube in each serving glass and pour prepared watermelon juice into it and serve chilled.
Notes
If you prefer plain juice and not the pulp, then I would recommend straining it.
But if you like it otherwise, then you are going to love the sweet taste of watermelon with a slight after taste of fresh lime.