Mix cold water and sugar. Chill until ready to use.
Wash limes with hand soap to get the wax and pesticides off.
Cut off ends & then cut each lime into eighths.
Place half the limes, & half the water/sugar mixture in a blender.
Pulse 5x. Strain into pitcher with a fine mesh strainer. Dump
pulp in trash. Repeat with other half of limes and water/sugar
mixture. Taste test and add more sugar if it's bitter at all.
Add condensed milk right before serving. Stir & enjoy. Best if
made right before serving.