A water source every three miles for 100 miles?
Aside from that, your post interests me because just the other day I was sort of daydreaming about the feasibility of running to my parents' new house, which is about 125 miles away. The route would be almost all back-roads with lots of little towns and small cities along the way. I've never run more than a marathon so I am in no way an ultra runner, but it would be an interesting adventure as a one-off.
I'm thinking I would do it in two days (I'm sure there's no way I can run 125 miles in one shot), with a night spent at a cheap hotel somewhere halfway along... but man, I can't imagine the aching legs would feel very good at the start of day two! That's well over two marathons back-to back over two consecutive days.
If I ever did do it, I would plan it out to ensure my route never goes more than around 12-15 miles at a time between at least some sort of place to purchase food/liquids, be it a convenience store, grocery store, gas station, whatever. A washroom would be a definite bonus.
I would bring a camelback-type hydration backpack with pouches to carry some toilet paper and some Clif bars/similar-type energy foods, and of course, money to buy food and whatever else along the way.