Strategy for handling the oddities that spew out of a fountain upon dipping

Solution 1:

One of the strongest defenses a low level character has is Elbereth. Before dipping, you can engrave one or more, just in case. If you're writing in the dust, you'll want to engrave it several times per square to counteract the quick erosion.

The other option is to run away. Note any doors you could close behind you. Be aware of all your escape options (Knights can jump away, for example). Also be aware of the stair locations. Running away won't do any good if you cut off your path to the rest of the dungeon.

Solution 2:

Against water demons, the best success I've had is to run away.

As for water moccasins, there is a reason why its one of the most common cause of death, not much you can do if you are surrounded at a low level.

These events are there most likely to help hinder fountain wish farming early on.