I would not say Water Fasting can cure EC, I would say it can help you figure out the answer to a very important question:
"If food, toothpaste and cosmetics are triggering your EC?"
During a normal water fast, you are not suppose to use any toothpaste, any soap, any shampoo, any deodorant, and any other cosmetics or medications or anything on your skin except clean washed cotton clothes, preferable washed without detergent.
Water only inside and Water only outside your body.
That way you eliminate most of the common EC trigger factors, except braces, pet dander, dust mites, pollen etc.