Crunchy potato wedges without oil is absolutely no rocket science. The most important thing is to let the potatoes soak in hot water. It releases some starch, and it absorbs moisture, which helps keep the potatoes crispy on the outside and tender and soft on the inside. If you want to go fast, you can also omit the step. The potato wedges just will not get as crispy as when you soak them. They still taste good. It's potatoes, after all.