How to Make It
Squeeze juice from lemons to equal 2 cups; reserve 4 squeezed lemons. Bring 6 cups water, sugar, and kosher salt to a boil, stirring occasionally. Remove from heat; add reserved lemons. Cool; strain into a large pitcher. Process watermelon and 1 cup water in a blender until smooth; strain into pitcher. Stir in juice. Serve with ice.