In a small saucepan over medium heat, combine the water and sugar, and boil until the sugar dissolves, about 1 minute. Remove from heat and allow to cool. Stir in the lemon juice and lemon zest, then pour into the bowl of an ice cream maker. Churn according to manufacturer instructions. When the sorbet has frozen into ice crystals (it will still seem quite soft), transfer to a storage container, cover tightly and freeze until ready to serve. The sorbet will solidify in the freezer.