Drain the canned potatoes well.
In a medium saucepan over medium heat add the water and the can of potatoes.
Heat the potatoes until the water is bubbling and keep heating till the potatoes are heated through. Turn the heat off.
Drain the potatoes again.
Set the pot back on the hot stovetop and place the butter, garlic and onion powder, parmesan cheese and sour cream into the potatoes. Mash well with a potato masher OR whip with a kitchen mixer.
Once mixed, if too thick, add the milk SLOWLY. Start with ¼ cup and then add by tablespoon fulls until desired consistency is reached.
Taste and add salt and pepper.