1In medium saucepan, stir together rhubarb, 1 cup sugar and the water. Heat to boiling; reduce heat. Simmer 15 minutes, stirring occasionally, until syrup turns bright pink.
2Place strainer over medium bowl or large glass measuring cup; pour hot rhubarb mixture through strainer into bowl. Discard rhubarb pulp. Pour syrup into jar or container. Cover; refrigerate 1 hour or until cold.
3Meanwhile, place 1/4 cup sugar on small plate or saucer. Rub rim of martini glass with lemon wedge. Dip rim of glass in sugar, slowly turning glass so only outer edge is covered; shake off any excess sugar. Place glass in freezer.
4To make 1 cocktail: Fill cocktail shaker with ice. Pour vodka and rhubarb syrup over ice. Shake 5 to 6 seconds. Pour into chilled martini glass, straining out ice.