I have not found that for me longer tours actually mean more weight carried assuming road tours in first world countries. I pretty much never need to carry more than 24 hours of food or water at a time. I always have clothing and sleeping gear to get me by in subfreezing temps any time I am in the mountains (my standard clothes and sleeping bag were fine when the overnight low dipped into the teens on my ST tour).

I don't count water or food in gear weight because they are variable throughout the day. I typically carry a couple bottles of water at the start of the day. Those occasions where I need to carry a gallon of water are pretty few and far between. When going ultralight, if I do need to carry much extra water it is usually carried in either jersey pockets or a small backpack. That has never been a big hardship since it doesn't happen that often and the load decreases through the day. If you were to tour somewhere that you needed to go several days between water sources the load would go up, but even on the ST I never found that to be the case.