Kibble, as commercial dry dog food is called, has almost all the water removed, it is dehydrated so that it keeps, it’s cheaper to transport (less volume) and easier for you to store at home. Nothing in that system is about the end consumer, your dog. The dog’s internal system has to re-hydrate the kibble in order to break it down and utilise it, the kidneys work the most, and the moisture must be taken from somewhere in the body.
My question for you would be around fruit. I know blueberries and strawberries are good for dogs, but my boy loves mandarin and banana too (I only give him very small portions)…. are these ok for dogs? Which other fruits are suitable/bad, and also recommended portions?