Interesting stuff—you may be fascinated by how we handle water shortages here.
I own a rural property with a deep pond. The property has long had an unwritten (not even hand-shake!) agreement with the local volunteer fire department that they can use a hydrant to take water from the pond as needed.
In addition there is a long (centuries old) tradition of sharing water from the pond with any local citizen who needs it.
Dry periods are rare here, but the local custom is that we share with our neighbors.
_Nothing_ is in writing—we are all very proud of that tradition—and there has never been a problem in the memory of the local elders.
Cheers!