Milk is a food and not a substitute for water. As a food, milk is incomplete and does not provide a balanced diet. It can be useful as a treat for some dogs, however, large quantities of milk may not be well tolerated.
Milk contains lactose, which requires the enzyme lactase for breakdown in the intestinal tract.
If the intestinal tract does not contain sufficient lactase, consumption of a high level of lactose can cause diarrhea in some pets. Repeatedly adding raw eggs to a dog's diet can cause a deficiency of the vitamin biotin. Some raw fish can cause a deficiency of the vitamin thiamine. Repeatedly adding raw fish to the diet of a cat is not recommended. Table scraps will not provide the balanced diet which dogs require.