Irrigation is a trivial matter. Look up some areal shots along the Colorado river between Laughlin NV and Yuma AZ. There are lots of crops grown in the worst of the Mohave Desert with water piped miles and miles from the river.
If plants can make use of that water, I'm guessing cows can as well.
I'm not saying it can't work, but it is expensive to pipe water miles and miles. Keep in mind that any Federal land crossed will subject the person running the pipe to many of the same criteria for siting an oil and gas pipeline in terms of biological, cultural, archaeological, etc. surveys, EIS, the works. I have seen that used against ranchers here by the BLM (Bureau of Land Management). God help you if you have one of those rare, threatened, or endangered things growing or living in there. Then you have all the problems/expense of maintaining a water system and pumps, which will require access to the river, anyway.
If you get enough money in the picture, anything can be done. But for now, you can let the herd walk to water, and that has worked for a long time.
As for 'trivial', "miles from water", consider used irrigation pipe runs 2 to 3 dollars a foot F.O.B. before it is set up and maintained. That does not include couplings or gaskets, and we both know a run on used piping will mean prices go up. This isn't a sprinkler system, it is a water pipeline to holding tanks. Most crops will do okay for 48 hours without a squirt, critters are more finnicky. Now that 2-3 dollars per foot might not seem like much, because many people think of ranches like the King Ranch or even Ted Turner's spread when they envision one, but for smaller operations absorbing costs gets more painful.
I don't know what sort of grazing density is considered 'normal' in South Texas, but that will affect how many miles of pipe are going to have to be run to replace just being able to let the cattle walk to water.
Out here, control the water, control the land. It has been that way since the first settlers appeared.
Anything
can be done if you have enough money to throw at it, but for some folks, that dog won't hunt. Again, the little guy gets squeezed by the big gummint changes. I have seen that somewhere before.