Some lawn grasses are naturally more drought-tolerant than others. Warm-season grasses such as buffalograss, Bermudagrass, and zoysiagrass need less water to thrive and survive than cool-season grasses such as fescue, Kentucky bluegrass, or ryegrass. Turf-type tall fescue and fine fescue are fairly drought-tolerant and will remain green through most summers. Kentucky bluegrass and perennial ryegrass go dormant and turn brown when conditions become hot and dry. Grass growing along sidewalks, curbs, and driveways dries out fastest and suffers the most.
If you don't care about keeping your lawn lush and green all summer, lightly irrigate with 1/2 inch of water every 3-4 weeks to keep the roots and crowns alive. This is not enough water to stimulate new growth, but it will keep the growing points moist enough to live. Avoid the temptation to give the lawn a soaking that could spur new growth, especially if you don't intend to continue watering. It's stressful to the grass to go in and out of dormancy. If you start watering thoroughly, continue to water thoroughly until rainfall returns to sufficient levels.