1. Combine and place covered in the fridge overnight. 2. The next day add 3/4 cup apple pectin stock (see link above for instructions) and a handful of under ripe berries of some sort if you've got them. I placed the berries in a muslin spice/tea bag. If you don't have the berries or the pectin stock, use unsweetened apple juice or frozen juice concentrate or just skip it altogether since the only reason it's in there was to achieve a possible jelly set.* (Next time I tackle a watermelon I'll probably tweak this syrup recipe to omit this step, but the syrup I ended up with tasted great, these ingredients included.) 3. Bring the mixture to a simmer to dissolve any remaining sugar granules. And then raise heat to med-high and boil for 10 minutes, stirring occasionally to keep sugar from scorching the bottom of your pan. Remove from heat and let it sit for 5 minutes before ladling it into a clean, hot jar. Let sit on counter to cool for an hour or so and then keep this in the fridge because watermelon is a low-acid food and this syrup recipe is not written/tested for safe shelf storage. *I realized once it was simmering that, since the watermelon juice is primarily water and contains hardly any pectin in the fibers remaining in the skimmed juice, I was cooking and skimming all the red and flavor out. Making non-added-pectin jelly with watermelon (and retaining watermelon flavor) wasn't going to happen, so I hopped ship and made syrup before I'd lost all watermelon flavor entirely.