I just checked on a webpage with agricultural information:
A typical milk cow needs around 25 gallons of water per day, in order to produce around 5 gallons of milk per day.
Noah's cows (and the rest of the ark's unfortunate inhabitants) would have died of dehydration in a very short time.
And this fundie's "argument" gets even more absurd when taking into account that as of the bible, there were only "two of each kind" on the ark. One male bull (which doesn't give milk), and one female.
So the milk supply would have consisted of one milk cow, one goat, one sheep. Roughly 7 gallons of milk per day in total. For an ark full with countless animals. Yeah right, that would have been plenty of water supply for every animal there...