I live east of Houston and just about have to mow twice a week. I do not water my yard but I do have a Hoot Aerobic System. So it does get that water.
That thin bermuda grass just doesn't do it for my yard. If I stood in my yard and could see dirt... I would have a problem with that... LOL
I think I know what your problem is in your picture now...

You can't see that thin grass.