[Chiyo had to think on that for a moment. She wasn't familiar with all the Pokemon of her world, just only those in Kanto and most of Johto and Hoenn. At the very least, she knew that not all of them had that ability.]

No. Not all of them, but there are a good many that can. For instance, the ability that allows me to change into my element is known as Acid Armor. Those that are able to use this ability will, essentially, be able to take on a water elemental form like you have suggested.