In a large pot over medium heat, combine the water and sugar. Cook and stir until the sugar has dissolved and the syrup looks clear, about 5 minutes. Remove from the heat and cool the syrup by pouring it into a bowl and putting it into the refrigerator or over an ice bath. Add the lemon zest and lemon juice; stir to combine. Mix in the lemon vodka.
Pour the lemon mixture into a shallow baking pan and freeze for 1 hour. Using a fork or a couple of chopsticks, break up all the ice crystals on the bottom and sides of the pan. This incorporates air so the final product literally melts in your mouth. Freeze for 3 to 4 hours, until the mixture has reached a frozen granular consistency. You can serve it two ways: Either rake the granita with the tines of a fork for a snow-cone-like product or run an ice-cream scooper down the length for a smooth Italian-ice-like result. Spoon it into a wine or martini glass.
Edited: October 12th, 2009