However, The Wall is the main reason I voted for Trump, although, other issues were important, too. I don't expect the wall overnight or in a year. I understand it will take years, but I am OK with that as long as these issues are being worked on to a resolution.
Makee ponds, canals, moats, whatever, on US side of wall. Makee deal with pump and pipe makers if necessary.
Good grief, there are at least 2 perched or partially perched lakes (2018 acre for the larger, fully perched cooling [power plant] lake, 450 acres for the smaller, created for waterfowl) within 3 hours drive of my home: Most of their water is pumped in from nearby waterways.
If we can pump water into 450 acre lakes for geese, or 2018 acre perched lakes for power plant cooling, we can sure as heck get water to cattle.
I suppose that they will pipe Rio Grande water into a long trough on the US side of the wall. To keep the water from going stagnant, they will have fresh water coming in from the river and going back out. Solar panels will power the pumps.
Maybe someone will invent pumps and plumbing. Could happen...