A few years ago some kind “granny” walked across america in order to support movement towards campaign reform. Other people have done this walk.
West of the Mississippi river, things become very dry. How do the walkers survive through say the mostly desert-scrubland of the south west? If they travel more northwards, they run into the relatively dry great plains. Are they walking hundreds of miles with only the supplies (including water) on their back? Or are they somehow cheating?
They buy water along the way. They can pick their route, you know. Nothing stops them from choosing a route which never leaves them for terribly long w/o a somewhat populated area
I’d imagine a supply van could factor in as well.
There’s also no rule that says the walker cannot be followed by a support vehicle which waits at strategic locations and supplies them with water and so on. Somebody that’s walking across the country for promotional purposes will probably have such an arrangement. It’s not really “cheating”, if the main point is that you are walking across the country. You didn’t say you were also foraging for sustenance along the way.
100+ years ago people went across the plains with horses and wagon trains and they all found water. Most of the the time they traveled close to rivers. Now people just travel from town to town.