Normally I get back to this forum more frequently, but this has been an unusual year of remodeling one house and moving out of another. My free forum time has been limited.
All lawns need an inch of water in the hottest heat of summer to look good. If you don't care about looking good, then you can go longer. When you go longer without watering St Augustine is going to wilt before you water again. Wilted St Aug will come back fine, but it's a lot of stress on the plant. Bermuda, on the other hand, may wilt but it seems to rebound much more quickly than St Aug. So St Aug is not really a water hog as much as it is more sensitive to drying out. If you leave it dry for the month of July, it might die and not come back with water. But I have left it dry for the months of September through December and it came back with water.
If you want to try something different, there is a variety of buffalo grass that has most of the good characteristics of a turf. The normal problem with buffalo grass is as soon as it's mowed down it sends up flowers and seed heads much faster than the grass grows. TechTurf (aka Turffalo) sends up the seeds and flowers but they grow at the same speed as the grass, so it doesn't look "hairy" in a few days. TechTurf also spreads like wildfire while normal buffalo spreads more slowly if at all. TechTurf becomes dense. Other buffalo grasses do not. Having said that the UC Verde buffalo hybrid is also a good alternative to the regular buffaloes. I have never seen UC Verde in person. TechTurf is a dense grass no matter what mowing height you like. The other issue with TechTurf is the color. It's a yellow green at its best.
Here's a picture of TechTurf that needs mowing badly. This shows the color and density. You can also see it escaping over the concrete.
Any other buffalo grass would have flower stems 8 inches high at this point.