Water and resupply are safety margins.
Running low on food is uncomfortable. Running out of water in a dry part of central or southern Alberta can become a serious problem quickly.
Do not assume that a creek shown on a map will contain usable water, or that a named community has a store. Route planning should distinguish between confirmed sources, seasonal or uncertain natural water, and places where water can actually be purchased or obtained.
Carry capacity should reflect the longest credible dry stretch plus a margin for delay. Heat, wind, reroutes, and slow surfaces can all increase the time between sources.