Depending on the type of lawn it is, you need a minimum of 1 inch per week (more if very hot weather) and ideally delivered all at once. Infrequent but deep watering is always preferred over more frequent but light watering. So it is not a question of how often but rather how much :-)

You can test how much water is being applied by placing a tuna or cat food can in various positions and measuring how much water accumulates after irrigation. Again, it is preferable if the necessary inch (or more) is applied all at once. And less frequent but longer, slower watering durations will encourage deeper root penetration and a more drought tolerant lawn. Learning how to water better means you will actually need to water less :-)

btw, NOW is the time to be considering aeration and overseeding! You are approaching the end of the window of best opportunity if you wait any longer.

Thanks for your thoughtful response. My lawn care company says it is too dry to aerate and overseed right now, which prompted my question. I agree that I should measure how much water the lawn is getting now, as some of the water may be evaporating more than when I measured last fall.

That having been said, for overseeding, you're going to have to water more often to get the seed to sprout. Seed that dries out is seed that dies.

Regrettably, lawns that stay wet are lawns that get fungal diseases.

You see the problem here.

For seed, it will need to be watered about three times a day (even if under most coverings) to keep it appropriately damp. Underneath compost, that may be less often, but more water--depending on the compost, of course. Two would be the floor number. One is not going to be acceptable under most conditions, but there are certainly some exceptions.

For how long that's required depends on the seed. In good conditions, rye usually sprouts in a week or so. Fescue, 10 days to 2 weeks. Kentucky bluegrass can be up to a month. Since you're talking about fall seeding, you've implied you have a transitional lawn and use northern grasses. Southern grasses will differ and are not generally fall sown.

Of course, that can be even longer if the temperatures are particularly hot or particularly cold, and the clock also stops if the seed goes dry (this will also quickly kill germinating seed, as mentioned above).

Post all that, cut back the watering slowly to let the new baby roots grow in, and let your adult lawn grow in roots it hasn't had to grow yet. Cut back to daily watering, then every other day in a week or so, every third day a week after that, and so on. See if it'll handle weekly watering the next year.

Some lawns will, some won't. It does depend on your soil, the organic matter levels (OM hold water like nobody's business, it's like a sponge), and the lawn.

I haven't watered since 2017 and mine looks good. Right now, we're 12 days with no rain and it's just starting to look dry in places, but my soil is tuned well for resources, the organic levels are kept very high, I keep it on the long side (short northern grasses are thirsty northern grasses), don't cut when it's dry (bleeding grass is grass that's losing water), and have bluegrass (one of the least drought-resistant grasses, actually, but it'll just go dormant if it does get droughty and come back when rains resume).

I live in Texas and did not water at all until mid June. Then I only watered the back lawn which is a hill facing to the south. The front was fine until July. How could I do that? We had about an inch of rain every month. That's month, not week. Since then I have been watering about once every 2 weeks, but I'm going to have to water the back today after only 1 week.

As the general temperature seems to be warming, I think Nashville is going to be in the northern part of the southern growing region pretty soon. The transition zone is moving to the north. I would think bermuda would be simple to grow in your area.

Gardengal's advice is great. You can set tuna cans out and time how long it takes your sprinklers to fill all the cans. Remember that time because that is how long you should water every time. If you get runoff before the cans are filled, then turn off the sprinklers and let it soak for 15 to 30 minutes. Then resume watering, and timing, until the cans are filled.

Generally once a week in the hottest heat of summer is a good starting point for deep watering. Once every 2 weeks is good with temps in the 80s. Once every 3 weeks should be good with temps in the 70s. Once a month with temps lower than 70. Sprinkler people LOVE to demonstrate the intelligence of their system by setting it to run far too frequently. By the way, my oscillator sprinkler takes 8 hours to fill the cans. Your in-ground system will do that much faster, but watch for runoff.