Add strawberries, watermelon, sugar and water to a large pan. Bring to a boil and lower temperature to low and simmer 5 minutes. Remove from heat and allow to cool 20 minutes. place in a blender or food processor, being careful because mixture may still be hot. Blend until smooth. Strain through a fine mesh into a container. Cover and refrigerate 6 to 8 hours or over night.

Mix fruit syrup with ginger ale and serve over ice.