Lay out 1/3 of the sliced potatoes followed by 1/3 of the sliced onions in a baking dish. Season with some salt, pepper and thyme.
Repeat previous step two more times to lay all the sliced potatoes and onion in the baking dish.
Pour the oil and water over the potatoes and season with some more of the salt, pepper and thyme.
Bake covered for 30 minutes. Remove the cover from the baking dish and cook for about 30 more minutes or until the potatoes are tender and cooked through.