Place water, oats, milk, butter, brown sugar, vanilla extract, cinnamon, and salt into an oven-safe bowl. Place the bowl into the bottom of a slow cooker. Fill the slow cooker with water up to the water level in the oatmeal bowl. Cover the slow cooker.
Cook on Low until oats are tender, 6 to 8 hours.
Stir in peaches with their juices. Cover and continue to cook on Low until warmed, about 30 minutes. Serve.