They seem to be most popular in Aguas Frescas (Fresh Waters)
Blender-up a good mash of 5-6 tunas. Force the mash through one of those large screened filters popular for making cafe de la olla. You'll get some pulp residue.
The liquid goes into a 1 to 2 gallon drink dispenser. Add purified water. The taste should be light duty not intense.
Some folks just add a light amount of sugar to tone-up the taste a tad.
I use La Madrilena sugar syrup for a more refined taste.
This isn't supposed to end up a potent sugary mix. Very light taste with a touch a sweetness.
This recipe works for all fruits and Jamaica flowers. With Jamaica I like the mix potent. Deep red and capable of puckering the lips. A strong taste relationship to cranberry (arandano).