Gather cold water, lime wedges, and sugar. Blend 4 cups of cold water with the lime wedges and ½ cup of sugar on high for 30-45 seconds until smooth.

Pour the blended mixture through a fine mesh strainer into a large bowl to separate the liquid from the pulp and skin.

Rinse the blender, return the strained juice, and add ¼ cup of sweetened condensed milk. Blend again for 20-30 seconds until smooth and frothy.

Fill glasses with ice cubes and pour the creamy mixture over the ice. Garnish with lime slices on the rim if desired.