Yes, a lack of water can cause them to become cannibalistic. As to Doggy Bag food, is that the dog food you're feeding them or does that company make a rodent food as well? I'm not familiar with Doggy Bag other than the dog food and I've only ever feed my rodents lab block and fruits/veggies with some dry cat food for the soft furs when they're nursing/pregnant, so I can't say on the food possibly being the cause. I know mice need a higher protein content than what do Norway rats, so you might look into that and check what percentage of protein/fat you're feeding them in their current food. Those are where I would start: possibly a lack of water and/or insufficient protein/fat in your current feed.