If you haven't had an agua fresca...well...you need to. They are yummy! Plus, they can cool you down and keep you hydrated. So how do you make them?
All you need is a blender, fresh fruit, and water! See? Easy! Start with fruit that's at peak freshness, or even a little overripe—if it's too mushy to eat, it's perfect to blend! Water-dense fruits, like melons, work well, but berries, stone fruit, and tropical fruits such as mango and pineapple work well too. Peel and cut the fruit into chunks, and then add it to a blender with equal parts water. In other words, one cup fruit + one cup water. Some people like to add sugar to their agua fresca, but if your fruit is in-season and sweet, there's no need. Watermelon is probably my first choice, but really, you can't go wrong.
Blend your fruit on high for 1-2 minutes, until it is liquefied. Then, strain over a large bowl using a sieve or cheesecloth to separate out the fruit pulp. Discard the pulp (or save for another project—like freezing it in small molds for a doggie-friendly sorbet). Cover and put the liquid in the fridge for at least an hour and up to three days.