Peel prickly pears: cut off the top and bottom and discard. Make a single cut lengthwise through the skin, cutting just deep enough to reach the fruit underneath. Use the cut to pull away the skin.
In a blender combine prickly pears, lime, sugar, salt, and 2 cups of water. Blend until smooth.
Slowly strain prickly pear mixture through a fine mesh sieve into a pitcher or bowl. Add remaining 2 cups of water and stir to combine.
Refrigerate until chilled. Stir before serving if separated and pour over ice.