The price of enjoying Mexico is vigilance. It is realizing that in everything you do, everywhere you go, each and every interaction you have, there is a hidden menace. An invisible threat.
Guarding oneself against the Aztec emperor's gastrointestinal curse means avoiding all non-treated water. This is not difficult, given the ubiquity of bottled water and alcohol, but it can make the enjoyment of aguas frescas an adventurous affair.
Aguas are like ades, made with fresh fruit, flowers, cacti, whatever. Often you'll encounter stands on the street with huge cylindrical jars of brightly colored aguas, looking superbly appealing in the Mexican heat. This is the time to be wary. Sip a careless vendor's wares and you'll find yourself perched atop the porcelain.
The agua de jamaica is made from dried hibiscus flowers, and is simple to the point of comedy. You simply boil the flowers (obtainable at most Latin markets) with sugar, strain over ice, and enjoy the tart, refreshing goodness.
The horchata is slightly more involved -- more ingredients and a certain amount of technique -- but oh the payoff. Horchata is one of the great accompaniments to spicy food: sweet, milky, and utterly delicious.
Recipes after the jump.