It seems to me that while water is the superior choice when it comes to beverages, I would not necessarily see it as an appropriate answer to the question.  I would interpret the question to be an inquiry about what could be used in place of cow's milk that has similar qualities or properties.  For example water certainly would not a very good substitute for cow's milk in many baking applications.

I would think that raw organic grassfed cow milk was a good suggestion and has been promoted on this web site as well as other reputable sites.  Also, raw organic goat milk is another possible alternative.

As far as using soy milk, there is far too many down sides to it for it to be a good candidate as a replacement.  That link that NaturalHealthLover offered is just one of many that explains why....

Zukas,

Humans aren't the only ones.

Cats drink cows milk, and enjoy it a LOT.  Tigers will suckle on a mother pig, and they end up being more gentle and end up healthier.  A Vegetarian Lion (Little Tyke) enjoys milk well into adulthood, and it praised as being the healthiest lion in existence.

What is wrong with eating the milk of other animal's though?  If the
Bible deems the animal unclean, then it produces milk that we should avoid.  But Lactating and drinking milk is beneficial for both parties.  A cow produces proteins, enzymes, and contains probiotics that are necessary for baby cows to grow.  Humans, who are biologically similar due to a common creator, thrive on the milk even though it is chemically inferior to milk of our mothers.  Should we avoid eggs completely because the yolk is what is used to feed a baby chick?  There are countless animals that eat eggs of other species.  Should we avoid all seeds (grains) because the endospore is what is used to feed the embryo?

Please look into this further.
...

I AM A FARM RAISED, OLD LADY AND THERE IS NOTHING LIKE FARM MILK!

While going to school in Colorado, early 80s, I again found farm milk and to my delight it was legal to purchase and sell.

Colorado has a law, presuming it is still in place, if the farmer will have his cows tested every six months and if they test "clean" then they can sell.

We enjoyed the cream and milk without the additives, we had energy and no health problems to speak of while in school.  We were all thin and full of energy.  Too, the farm made better money and I was and still am for that!

What we drink now does not contribute to the necessary actions of our bodies to do their jobs, like fire off enzymes for digestion, to help protect against disease, etc.  We found, on the raw milk, we ate less and enjoyed it more, which brings up another point.  The foods we buy at market, just how safe are they and how nutritious?  I firmly believe that artificial fertilizers do a great disservice in this area and with that said, farmers are selling out to the thousands of acres per year.  How are the children and grandchildren going to survive, take a pill?  I suspect the taste buds will have something to say about that plan!
...

The best choice, which we recommend to our  cancer support  members, who are taking our cancer recovery course at www.friendswithcancer.com.au  , is goat  milk .... I am a recoverer myself , and an avid follower of Dr. Mercola,  and  as this is my 9th year of good health I say this ......
....who am I to ignore Proverbs 27 v 27  "and you shall have goat milk for you food, for you household and ( I like this part) for the maintenance of your maidens. "  We buy it pasturised from Woolworths....

How about nut milks? I use unsweetened almond milk by Blue Diamond to cook with or make smoothies, any time a recipe calls for milk....