Combine orange, pomegranate seeds, and 1 cup water in 8-cup liquid measuring cup or large bowl. With potato masher or muddler, muddle fruit until broken down and all juice is expressed, about 30 seconds. Stir in 3 cups water. Cover and refrigerate until flavors meld and mixture is chilled, 30 minutes to 1 hour.
Strain infused water into pitcher, pressing on solids to extract as much juice as possible. Discard solids. Stir in remaining 4 cups water and garnish with extra orange and pomegranate seeds. (Water can be stored in refrigerator for up to 1 day; garnish with extra orange and pomegranate seeds just before serving.) Serve in ice-filled glasses.