Like most seeds, grass seeds need to drink water to come alive. Moisture hastens growing time and promotes a healthy lawn. On a dry planting day, soak your newly sown grass seed with a hose or sprinkler; save money and time by simply waiting for a rainy day to sow.
Grass seed sown on dry soil can blow away in the wind or be gobbled up by birds. Moist or wet soil helps seeds stay put.
Although a good rain is a good thing for a freshly-seeded lawn, too much may not be so beneficial. Heavy downpours and flooding can wash your grass seed away to a place where it will sprout eventually but probably not where you would like it to sprout.