01 - Place quartered limes in blender with 2 cups cold water. Pulse 5–7 times—do not over-blend to prevent bitterness.
02 - Strain mixture through fine mesh sieve into pitcher, pressing firmly to extract all liquid. Discard solids.
03 - Add remaining 2 cups cold water, sweetened condensed milk, and sugar to pitcher. Stir until sugar dissolves completely.
04 - Taste and adjust sweetness if needed by adding more sugar.
05 - Serve immediately over ice, garnishing with fresh lime slices if desired.