Quarter 5 small limes and place them in an 8-cup blender with 4 cups of water.
Blend for one minute on high speed to extract the flavorful oils and juice from the limes.
Place a fine-mesh strainer over a large bowl and slowly pour the lime mixture through it.
Using a rubber spatula or large spoon, press the lime pulp left in the strainer to extract as much juice as possible.
Rinse the blender and add the strained lime juice mixture back to it.
Add the remaining 2 cups of water, 1 cup of white sugar, and 7 ounces of sweetened condensed milk to the blender.
Blend on low for about 1 minute until everything is thoroughly combined.
Gently scoop off the foam from the top if desired (this is optional based on texture preference).
Serve immediately over ice cubes with lime slices as garnish.
Notes
Lime Selection - Choose limes with thinner skins to reduce the amount of white pith, which can make your drink bitter. The rind contains essential oils for flavor, but too much pith creates bitterness.
Blending Time - Don't over-blend the limes in the first step. One minute is sufficient to extract the flavor without releasing too much bitterness from the peels.
Straining Technique - Take your time when straining to ensure you remove all the lime pulp and pieces of peel. This step is crucial for a smooth, enjoyable drink.
Temperature - For the most refreshing result, use cold water and serve immediately over ice. If making ahead, chill thoroughly before serving.
Sweetness Level - Adjust the sugar to your taste preference. The recipe creates a balanced sweetness, but you can add more or less depending on how sweet you like your drinks.