dill pickle recipe

4 cups water - 1 1/2 cups white vinegar - 1/4 cup granulated sugar - 2 tablespoons kosher salt - 1 pound pickling cucumbers, washed and sliced - 4 cloves garlic, peeled and smashed - 2 teaspoons mustard seeds - 2 teaspoons black peppercorns - 4 sprigs fresh dill - 1/2 teaspoon red pepper flakes (optional