In a blender, combine the cold water, limes, and granulated sugar. Blend on high for about 30 to 45 seconds until smooth.

Pour the blended mixture through a fine mesh strainer into a large bowl or pitcher, pressing to extract juice while discarding pulp.

Return the strained liquid to the blender and add sweetened condensed milk. Blend on medium speed for 20 to 30 seconds until smooth.

Fill tall glasses with ice cubes and pour the creamy lemonade over them, garnish with lime slices or mint leaves if desired.