Begin by cutting a ripe watermelon into uniform cubes, spreading the cubes in a single layer on a parchment-lined baking sheet. Freeze for about 4 hours until solid.

Once frozen, gather a high-powered blender. Add frozen watermelon cubes and lemon juice. Blend until smooth, adding water if the mix is too thick.

Taste the sorbet and add sugar if desired. Blend again briefly to mix.

Transfer the mixture to an airtight container and store it in the freezer for up to 3 months.