Here's one little thing I noticed about lawn maintenance with regards to water. After the recent heat, I watered my lawn, and it helped a little bit. Then, a couple of days later it rained, and this made a huge difference.
The reason? As far as I can tell, it is the fact that rainwater contains oxygen. I saw a product the other day, "Pure Rain", that supposedly can oxygenate regular water coming out of a garden hose. Whether it works or not, I don't know (the product was on clearance, so maybe not).
Overall, this would show that typical lawn watering is inefficient because you are not giving the grass the type of water it needs for proper growth.