Connect a garden hose spray nozzle with a "mist" setting to a standard garden hose. Use the hose to distribute a fine sheet of water over the grass seeds of a newly established lawn. Water each section of the lawn for 4 to 5 minutes, or until the top inch of soil is evenly moist.
Repeat this process two to three times a day depending on the weather. On hot, windy days, seeds may need water every few hours to stay moist, though grass seed sown in shady areas will not need as much water as those exposed to full sun. Once the grass is up, reduce the schedule, watering every other day for 10 to 15 minutes until the grass has reached 2 inches in height. At maturity, water grass weekly for 30 minutes at a time.
Fill a watering can and hand-water seeds that you have scattered over bare spots. Water until the surrounding soil is wet, not waterlogged. Repeat the process two times each day until the seeds sprout.
Scatter sprinklers across the yard to water an over-seeded lawn. Normally, it is best to give the grass a thorough soaking once a week. However, to get the new seeds to sprout, you will need to water twice a day. Turn the sprinklers on for 5 to 10 minutes first thing in the morning and once again in the afternoon. When the seed sprouts, reduce the schedule, returning to weekly watering for 20 to 30 minutes.