Bring water, sugar, and lemon zest to a boil in a 1-quart saucepan, stirring to dissolve sugar, then boil 5 minutes.
Transfer to a bowl and add pomegranate and lemon juice, then chill until very cold, at least 1 hour.
Just before serving, pour pomegranate syrup into a 2-quart glass pitcher and add champagne.
•Syrup can be made 2 days ahead and kept chilled.•To squeeze juice from fresh pomegranates, halve them horizontally and squeeze them, like oranges, with a reamer.
