Place the ice cubes into a half-gallon pitcher and layer the lemon slices on top.
In a separate bowl or container, thoroughly whisk the lemon juice with the sweetened condensed milk until smooth and well combined.
Carefully pour the creamy lemon mixture over the ice and lemon slices in the pitcher.
Top off with the cold water and stir thoroughly to ensure all components are evenly mixed.
Serve immediately and enjoy the refreshing taste.