Gather seeds from watermelon and place in colander. Be sure to use only the black seeds. Do not use the small, white seeds. Rinse thoroughly in colander to remove any excess watermelon. Once clean, spread out in an even layer on a cookie sheet and allow to dry. Drying outdoors in direct sunlight is a good method. Seeds can be patted dry, but roast much better when they are completely dry.
In a frying pan on the stovetop, place watermelon seeds on medium high heat and turn until seeds are roasted. In a cup of water, add salt and stir until dissolved. Pour salt water into frying pan and stir occasionally until water has evaporated. Once done, allow seeds to cool completely before shelling and eating.
Watermelon seeds can also be toasted in the oven at 325 degrees for 15-20 minutes. Wash and dry as above. Spray seeds with cooking spray and sprinkle evenly with salt. Allow to cool completely before eating.