Watermelon Juice: Remove the rind from the watermelon and cut into chunks. Blend until smooth, then strain through a fine mesh strainer. Stir in the salt until dissolved. Refrigerate for up to 1 week.
Jalapeño Cucumber Syrup: Combine the sliced jalapeños with ½ cup sugar and let macerate in a covered bowl for 6 hours. In a separate bowl, combine the cucumber with the remaining ½ cup sugar and let macerate for 4 hours. Simmer the jalapeño mixture with the water for 10 minutes, stirring frequently and avoiding a boil. Cool for 15 minutes, then blend with the macerated cucumber. Strain through a fine mesh strainer. Refrigerate for up to 2 weeks.
Jalapeño Salt: Finely grate the jalapeño into the sea salt and mix well. Spread onto a baking sheet and bake at 250°F for 30 minutes, or until completely dry. Cool before storing.
To prepare a cocktail, rim a Collins glass with jalapeño salt and fill with fresh ice. Shake bourbon, watermelon juice, jalapeño cucumber syrup, and lime juice with ice. Strain into the prepared glass and enjoy.