Eruvin 20: Watering the Animals

Note: Apologies for the interference from Yardaena's outdoor setting to record. Setting an enclosure around a well from before Shabbat - what if it dries up over the course of Shabbat? Or dries up and then is filled again by rain, both over the course of Shabbat? Namely, the status over Shabbat has shifted from what it was at the beginning of Shabbat. Does that change the standing of the enclosure? Is the eruv legitimate, insofar as permitting carrying? The need for access to water clearly made the enclosure necessary, but that only makes sense when the water is in the well. Another question - how close to the well can those boards be? Maintain your presence in the private domain even if you take a swig from a public domain. But is that the same concern for an animal who is partially in the public domain, and partially in the private? Will the animal wander away? Will the animal bring its trough to the other domain? In a nutshell, what do you do when variables that can't be controlled come into play? Once they permit some measure of this eruv, they work to limit how far the leniency goes.