Place the watermelon, strawberries and honey in a blender and puree until smooth. Add water if necessary to puree.
Pour watermelon/strawberry juice into a freezer-safe container or dish and freeze until firm, about 4 hours.
Video
Notes
Sweetener: Adding sweetener is optional. Fruit tends to taste less sweet when frozen compared to its fresh state. If you choose to add a sweetener, about 1/4 cup of honey usually suffices.
Blending: The type of blender you use may affect the need for additional liquid to help puree the fruit. While a high-power blender like a Vitamix typically requires no extra water, using a less powerful blender might necessitate adding a few tablespoons of water to achieve a smooth puree.
Serving Dish: Any freezer-safe dish can be used to freeze the sorbet. I often use a 5x5-inch baking dish, but feel free to use whatever you have that can comfortably hold the mixture.