This may seem patently obvious, but grass seed needs water to grow. I know, I know, I'm not exactly challenging your intellectual thinking skills. I often wonder if the general populace really gets this stuff, and I'm only privy to the small sampling of people to whom logic cannot stick. I engage in the following question and answer series more times in a year than you can imagine.
Q: I have lots of bare patches in my lawn, what can I do to fill them in?
A: Seed them, or have a company seed them for you. Make sure to water daily until they fill in.
Q: Okay, but I can't really water. The property is too spread out and I'm on a well that we don't want to stress.
A: Okay.
Q: So, what can I do?
A: Pray for rain.
Q: What if it doesn't rain?
A: Try to water.
Q: But I can't.