Use a blender or food processor to purée the fruit, sugar, and lemon juice if you’re using it; add 1 tablespoon water at a time as needed to get the machine going.
Divide the liquid evenly among plastic molds or small paper cups. Freeze for about 45 minutes, then insert a wooden stick into each; the pops will have frozen enough that the stick will stay upright. Freeze for another 2 hours or until solid. These can stay in the freezer for up to 2 weeks; any longer and they may get freezer burn. Run the molds or cups under cool running water for a few seconds to loosen the pops and serve.
Purée 2 cups chopped seeded watermelon and 124 cup lightly packed fresh basil leaves with the sugar and lemon juice.
Cucumber-Melon Pops
Purée 1 peeled and seeded small cucumber and 1 cup chopped honeydew melon with the sugar and lemon juice.
Mango-Coconut Pops
Purée 1 1/2 cups chopped mango (push it through a fine-meshed strainer if you want to remove any fibers) and 1/2 cup coconut milk with the sugar and lemon juice.