Much of the work available to the undocumented is seasonal. Those who don't find other work quickly will go back home to Mexico until the work is available again. Then once again they will run the gauntlet to find work in the north.
Without enough safe drinking water they're very likely to become what the Border Patrol calls a "Juan" or "Maria Doe". Since Operation Gatekeeper and Hold the Line (1994), an estimated 3800 plus crossers have joined the "Doe" family, over two-thirds of these from dehydration.*
* In some cases cause of death is unknown. In other cases bodies are unidentifiable, dismembered by animals.