Squeeze the lemon juice into the pitcher, then use a whisk to incorporate the sweetened condensed milk. I like to start with 5 lemons, and then add more if needed.
Slowly add the water, stirring to combine well. You could also combine the lemon juice and condensed milk in a small bowl first, then add it to the water in the pitcher. Either way works!
Taste the lemonade before adding ice. If you aren't sure about the sweetness, you can always start with a little less condensed milk. It's easy to add more, and whisk it in. You also may prefer it to be more tart, or more lemon-y, and this is the perfect time to adjust to your liking.
Once you have it the way you like it, add the ice. Slice a few lemons and float them on top. You're ready to serve!