You have to have access to Water during an extended survival event. That's a fact. You should also have a means of storage, and transport. If you're surviving in place, you have a lot of options. In this instance, we are talking about portable Water containers and storage options. Think Canteen and Water Bottles, and perhaps a Collapsible Water Container for storage and/or the transport of your Water from the source to your campsite.
You might be fortunate enough to be immediately adjacent to a Water source, but you shouldn't count on it. You may be forced to walk a significant distance in order to secure survival Water.