Currently, when you kill/shutdown znc, and then reopen it, it forgot the list of entries of the watch module.
The idea is to save this list somewhere :)
Quite old, but this feature still isn't avaiable :(
(I mean, you have so many modules that save the settings, why not this one?)
This has been implemented with r1304 on Dec 26 2008 (= quite a while ago).
Finally closing this now...