In a saucepan, bring water to a boil and stir in sugar and salt until dissolved. Cool.
Add lemon zest and juice.
Pour into 2 metal ice cube trays with dividers removed, or a metal bowl, or a 9-inch square baking pan and freeze.
After about 1-1/2 hours, remove from freezer and rake a fork through the ice, to fluff it up.
Return to freezer for about 2 hours.
Remove from freezer about 20 minutes before serving, so ice is easy to scoop.
Tips
An easy way to zest a lemon is to use a grater with small holes and grate the peel off the lemon directly over a bowl to it. Be sure to use only the colored part of the peel. 1 lemon yields approximately 1 tablespoon zest. Zest is best grated fresh and used immediately.