I am posting a new recipe for Brazilian Limeade because I have fine-tuned it. You can find the old one here, if you are interested.
The recipes are mostly the same, but, now that I live in the south, it is easy to find key limes, so I no longer use regular limes. Not to mention, they are cheaper and taste better. Also, I found these small cans of sweetened condensed milk called "La Lecherita" that are one-quarter the size of a big can (3.5 oz). Now, when I make limeade, I don't have an open sweetened condensed milk can going to waste in my fridge. You can find them in the baking aisle and I have also seen them in the Mexican aisle.
I think either recipe is good, but I prefer this one.
4 c. water
8 key limes, quartered
1/2 c. sugar
3.5 oz sweetened condensed milk (La Lecherita)
Put all ingredients in blender and blend! Strain through fine strainer. Serve immediately over ice.