it seems bugged then,
Because if it doesn't share food and water then that makes supply lines extremely simplistic. Also why would they add water purifiers that add like 40 water to a settlement if the max number of people in a camp is like 20-21. That's extremely overkill.
I really do hope they mean to fix this, because if supply lines are only meant for crafting materials you essentially made a perk that works only for superficial aspects where it could be something really cool.
Imagine having a settlement that deals with farming/water supply for the rest of your settlements, then having another one that works as a central hub and a quick connection to settlements in other locations, and another one that is almost exclusively meant as your commercial settlement.
I wanted to make this crazy Las Vegas-type settlement, with make-shift hotels and everything, that would get its food/water from other camps. If they don't share food and water though I don't think I'll put too much effort into making my whole network of cool commercial camps. And I guess this also means I won't be putting any effort into the system. I already have my central hub and a second settlement. That's good enough for now.
That's because any excess water gets bottled and put into your workshop? Then that counts as "supplies" and therefore gets transferred between settlements?