Wash the limes thoroughly to remove any dirt or wax on the skin.

Cut the limes into quarters, leaving the skin on.

In a blender, combine the lime quarters, cold water, and sugar.

Blend on high for about 30 seconds, just until the limes are broken down. Avoid over-blending to prevent a bitter taste from the lime peel.

Strain the mixture through a fine-mesh sieve into a pitcher to remove the pulp and peel. Press the solids gently with a spoon to extract as much liquid as possible.

Stir the sweetened condensed milk into the strained lime mixture until fully combined.

Serve immediately over ice cubes for maximum refreshment.