I learned this from some great Brazilians, the Pachecos, that were in an Orem ward with us. It has always been a favorite drink of my kids' and I love serving it whenever we cook Mexican food. I usually make a ton of it.
1/2 c. sugar
2 T. sweetened condensed milk
3 c. water
Wash the limes thoroughly, cut off the ends and cut into wedges. Place into the blender with all the other ingredients. Blend for approximately 10 seconds. Strain through a fine mesh strainer to remove all the rinds and pulp. It can be made ahead and put in a pitcher, in the fridge, until ready to serve.