Dogs lose water through urination, panting and sweating. It is advised to fill your dog's bowl at the same level so that you can monitor weather your dog is drinking too much which may indicate an internal illness.
Although canned food does contain liquid, this is not a factor or consideration for a dog's daily water intake.
Avoid encouraging dogs to drink out of the toilet as monitoring drinking habits may be difficult. Put the seat down after each use. This will force the dog to receive his water from his designated water dish.
Luv Sheila & Freedom (my black lab)