Combine the water and sugar in a small saucepan and cook over medium-high heat, stirring, until the mixture comes to a boil and the sugar has dissolved. Let cool to room temperature.
Cut the avocados in half lengthwise. Remove the pit and scoop the flesh into a blender, along with the cooled syrup and salt. Blend until smooth, scraping the sides as needed. Add the lime juice and blend just until combined.
If using conventional molds, divide the mixture among the molds, snap on the lid, and freeze until solid, about 5 hours. If using glasses or other unconventional molds, freeze until the pops are beginning to set (1 1/2 to 2 hours), then insert the sticks and freeze until solid, 4 to 5 hours. If using an instant ice pop maker, follow the manufacturer's instructions.
Reprinted with permission from Paletas: Authentic Recipes for Mexican Ice Pops, Shaved Ice, & Aguas Frescas by Fany Gerson, copyright (c) 2011. Published by Ten Speed Press, a division of Random House, Inc.