My biggest concern when I was planning this long ride was how I would ensure that both Apollo and myself can stay sufficiently hydrated. While there are ways to carry water on a saddle, doing this would add far more weight than any other item. At approximately 8 pounds per gallon, even adding 1 gallon would increase the typical pack weight (or dead weight) by 10%, which is a significant increase. A horse will drink 5 gallons per day minimum; a hardworking long ride horse will drink far more than that! There is no way I can add that much water to the pack and be able to ride Apollo too.
For populated areas, even rural farmland, there will be sufficient opportunities to stop along the way and access water at private homes and ranches. Since I've planned my route to stick as much as possible to places where people live, this will prevent me from needing to carry more than an emergency ration of water for most of the ride. This is how my mentor Lisa accomplished her solo ride without carrying water.
There will be some areas where water may not be readily available. In those areas I will have to be extra-careful to schedule each day's ride on a route that will pass by residences, or at least stock tanks in extremely rural rangeland. Creeks and other natural water sources will be available in most of the wildnerness areas through which we will need to pass. It is likely there will be a section or two where there will be no water at all for a day or two; should this be the case, I will be able to pack minimal water rations to get us safely (if not comfortably) through these deserts.
With some careful planning and friendly neighbors, we'll make it happen!