Quick answer: About 1 inch of water a week, deep and infrequent, applied in the morning. Warm-season grass can go dormant through a dry stretch and bounce back; Tall Fescue needs more consistent water. Piedmont clay soil means cycle-and-soak watering beats one long soak for anyone with an irrigation system.
Three questions, three pages
Watering a Piedmont lawn well comes down to three separate questions: how much and when to actually water, whether an irrigation system makes sense and how to run it in clay soil, and what to do differently when a real drought or a watering restriction hits.