Originally, I made this cocktail with a popular, pre-sweetened brand of cranberry juice, BUT... now I use a natural non-sweetened juice, so if you use the popular brand, your drink will not be as dark as the one I make here. It is because the juice I use is a more robust, purer juice. I'll keep the photo of my original watermelon cosmo at the bottom of this post so you can see what to expect.
If you opt to use pre-sweetened cranberry juice, OMIT the simple syrup as it would make it too sweet.
If you don't want to infuse your own vodka, you can usually find different brands that make a watermelon vodka like Veil, Skyy and Smirnoff in the liquor store.
Although the vodka in the old photo below is pinkish, if you infuse your own vodka, you won't always get that result. The vodka I infused for the new photos has a different tinge. Don't be alarmed, it all tastes delicious.
If you are just washing a few limes, use a natural, unscented hand soap and rub your hands with the soap over the fruit. Run cold water over the limes as you use a vegetable brush on the skin.
Make your own simple syrup as it is easy. Here's how: measure equal parts of water and white sugar and place in a sauce pan, turn the heat on medium and bring the mixture to a boil, stir, then lower to a simmer for 5 minutes. Cool completely before using.