Combine base. Add the sweetened condensed milk to the bottom of a large pitcher, then pour in the lemon juice and whisk well, making sure to scrape the sides of the pitcher.
Add ice and water. Fill the pitcher with ice cubes, then pour in cold water until the pitcher is full.
Mix. Stir thoroughly with a long spoon or whisk until evenly combined.
Serve. Pour into glasses and serve cold, optionally garnished with fresh lemon slices.
Notes
Substitutions. Condensed coconut milk or full fat coconut milk can be used for a dairy free version.
Recipe Tips. Use sweetened condensed milk, not evaporated milk. For a sweeter drink, add ¼ to ½ cup granulated sugar. To get more juice from fresh lemons, microwave for 10 to 30 seconds and roll before slicing. Lemon concentrate can be used to boost lemon flavor.
Storage. Refrigerate for up to 2 to 3 days and stir before serving if separation occurs.