yes, any container that has a chance to drop water, backpacks, urns, etc will drop your level of character water, in addition has a chance to drop lorkhans tears.
Just did a quest with a level v9 and came out with 34 lorkhans tears, spoilered it on one of the other threads about it. ZOS did a really good job with this, they thought way ahead, it just requires you to work for your writs, which is only natural if you ask me.
Want the final writ, top notch? Sure here it is, work for it, because thats what being a master craftsman is all about, work. Cheers for ZOS.
Not to mention they made all the lootable containers that everyone skips because its crap anyway worthwile looking into just because it might have that thing you need to complete writs. if any update in any game was successful this one certainly is.