Combine 1 cup water and sugar in a medium saucepan over medium heat until the sugar is dissolved. Cool to room temperature.
In a large pitcher, combine cooled sugar water, lemon juice, pomegranate juice and remaining 3 cups of water. Stir to combine. Just prior to serving add sparking water.
Garnish with pomegranate seeds and lemon slices, as desired. Keep chilled or serve with ice.
Notes
You can substitute store bought lemonade for the water, sugar and lemon juice. But I highly recommend making your own lemonade. It will result in a more fresh and flavorful drink.