Combine 1 cup water and sugar in a saucepan and bring to a gentle simmer over medium-high heat, stirring often. Simmer until sugar is dissolved. Remove from heat and allow simple syrup to cool.
Cut off pineapple crown and remove the outer skin. Cut pineapple flesh into chunks and add to a high-capacity blender (such as Vitamix). Pour in 2 cups water and blend until liquefied.
Pour liquefied pineapple juice into a pitcher. Add remaining water, lemon juice, and simple syrup. Stir before serving.