Solani, your recipe for ACV is something I've looked for for about 20 or 30 years! I've seen many recipes, but they have ingredients that IMHO don't belong. This one is straightforward.
I do recall reading a recipe years ago for watermelon vinegar and it looks nearly identical to yours. I recall the recipe saying to cut the watermelon in chunks, and place in large glass jar, cover with cheesecloth, but I thought it said to place it in the sun. Somehow that didn't seem right, so glad I didn't do it. But now see how easy it would be to also make watermelon vinegar, just substituting, and using your recipe. Maybe that will be a project for this summer. WCV. LOL