Here's the recipe--it's as simple as you can get:
2-3 cups fruit (cut up, mashed, or sliced)
3-4 cups water
1/2 - 1 cup sugar
Place fruit in the blender with the sugar and fill to the top with cold water. Blend until you have a liquid consistency. Serve with ice, if desired.
We make this all the time, using whatever fruit happens to be in season. Right now our favorites are watermelon (sandia) and strawberries (fresa).
Note: you can good deals on fresh fruit by visiting hispanic supermarkets.