http://www.straightdope.com/classics/a1_358.html
Apparently, this was common in 1976, but, I have to say that I have never seen a chocolate chip cookie recipe that has called for water. Did Cecil’s column convince recipe writers that this was unnecessary after all? If the water did have a beneficial effect (making the batter more docile), then why is it left out today? Curiouser and curiouser…
I just made a batch of Ghirardelli chocolate chip cookies not too long ago, and the recipe on the bag called for water. However, I forgot to add it in, and as Cecil said, the only difference I noticed was the dough being a little harder to work with. Cookies came out great 
… you guys should have asked a food scientist about this one. or a grandma. cookie recipes (and many other old recipes) used to list the ingredients by weight. one used an ounce of this, a pound of that. in fact, pound cake is so named because of the original recipe which involves a pound each of the necessary main ingredients (butter, flour, etc.). when recipes were passed on and written down in cookbooks, it became more common and universal to measure out the liquids in cups and teaspoons, etc., and the flour and such was measured in cups, ounces, etc. that “extra” teaspoon or half-teaspoon of water is not “extra” at all. it simply makes up the equivalent measure of the original recipe as converted to commonly used measures today, such as cups and teaspoons, which don’t convert evenly into measures of weight rather than volume. a cup is a measure of volume. a pound is a measure of weight. picky old-school bakers will tell you that measuring baking ingredients by weight is much more accurate and still the prefered method if you’re truly serious about your cookies!! hence the “weird” amounts when you convert grandma’s cookie recipe into cups and teaspoons.
Two mistakes there, nyxmuse. First, we’re not asking why there’s an “extra” spoonful of water. That’s the only water (as such) that’s in the recipe at all. It’s not like the recipe is calling for 1 cup + 1 teaspoon of water; it’s just calling for one teaspoon, period. And in any event, water, of all substances, does convert exactly between volume measure and weight measure. One fluid ounce is the volume of water which weighs one ounce, and the rest of the units follow from there.
But the second, and more greivous, error is that Grammas don’t measure ingredients by weights or volumes. They measure by a handful of this, a pinch of that, just the right amount of the other, and enough of the rest that the consistency is right. Which, empirically, seems to be a very good way to measure ingredients, judging by the outcome of the typical gramma’s cooking.