Mix water and sugar together until sugar is dissolved. Put in the fridge to chill until ready to use.
Use soap and water to thoroughly wash the limes. You want to scrub really well because you are going to be using the whole lime! After you've washed and scrubbed your limes, cut the ends off the limes (DO NOT MISS THIS STEP!) and then cut them into eighths.
Place half of the limes and half of the sugar water in your blender and pulse 5 times. Strain through a fine mesh strainer into the pitcher that you are going to serve it in. Discard the pulp. Repeat with the second half of your limes and sugar water. Mix in the sweetened condensed milk. Serve over lots of ice.
*A Couple Of Notes From Our Favorite Girls Over At Our Best Bites
When picking your limes, try to pick out the ones with the thinnest, smoothest skin possible. Supposedly they are less bitter and the most juicy. If you do end up with a more bitter drink, add more sugar and maybe even a little more sweetened condensed milk to taste.