Pour the water into a pot. Slice the lemons in half, squeeze the juice into the water, and drop the rinds into the water. Add the parsley, celery seed and cayenne pepper. Bring to a boil, then let the tea steep for 1 to 2 hours. Filter out the solids and store in the refrigerator. Reheat as needed. If you need a little more sweetness, add a few drops of stevia.