"Water deeply and less frequently" should be your mantra for summer watering of your lawn and all your other plants. Deep watering encourages deep root growth. When irrigating, be sure the water penetrates down to a depth of six to twelve inches.
Know how much water your sprinkler system puts out. I recommend placing three or four tin cans (or other flat bottomed, straight sided containers) across the section of lawn to be watered. Run the sprinklers for 30 minutes and measure the depth of the water. You want to spray a minimum of 1/2 to 1 inch of water over your lawn per irrigation cycle. So if thirty minutes puts down 1/4" of water, you'll need to keep the sprinklers on for at least an hour. Look at the grass before you water. If the blades are narrow (folded length wise) and grayish-green in color it's time to water. If the grass is nice and green, wait a few days. It all depends on the daytime temperatures.
Buffalo and Blue Grama grass lawns need about 2 to 3" of water per month during June, July and August. So a once per week soaking is recommended if there's no rain. Get a rain gauge for your house. This way you'll know how much came down and whether you need to add some more water or not.
When you mow, leave the grass long. The worst thing you can do to your lawn during the heat of summer is to scalp it by mowing too low. Adjust the deck of your lawn mower to leave the grass 3 to 4" long. This allows the lawn to shade its roots and reduce the frequency of supplemental irrigation.
Summer is a great time to plant Dog Tuff™ and Legacy® Buffalo grass plugs. The summer heat is what makes the plugs grow rapidly and fill in quickly, as both varieties are warm season growers. The key is to have a reliable water source so you can keep the plugs adequately moist as they get established.