They say that the best way to exorcise worries is to talk or write about them, and so I will, given that you got me thinking about drowning, a … sensitive subject for me, for no rational reasons whatsoever. So I’ll give you my insights as a Bringer of Death instead of sending my Scuttering Squad to give you a, let’s say "personal lesson".[li]
First of all the basics:
Humans in the Neath obey by the same biological rules of those residing in the surface, they need to breathe, to eat, to have their internal organs intact and they react poorly to pieces of metal encountering their flesh thanks to a sufficient kinetic force (bullets).
The problem arise because they don’t stay dead, because for certain reasons Death is usually temporary in the Neath.
There are 2 "exceptions" to this rule: Drownies and the so called Tomb Colonists.
For reason unknown drowning is something that you can’t just shake off, and has permanent effect on the ones affected.
Drownies can still talk, reason, they are not "zombies" but are particularly dangerous because they seem to possess a desire to inflict their fate on others, with the added benefit of boosting their ranks, but they do not persecute this objective excessively, seemingly more interested in keeping away from society.
They also seem to acquire some kind of arcane knowledge, see "Drownies’ Songs", but of that I don’t know much.
I see no reasons why the place of death should have any difference, be it shallow or deep water.
Tomb Colonists are the result of some kind of very grievous injury, like a devastating blow to the head. They are still "alive", capable of feeling the full range of human emotions but they seem to be bored most of the time, bar a few notable exceptions.
Tomb Colonists seem to be in some state of decomposition, as they tend to give fouls smells, or smell of formaldehyde and they seem to lose pieces.
They can be put down again, for example by sustained rifle fire, but they are a bit hardier than "normal" humans.
There are ways to kill someone permanently:
If you die of natural death or of illness you don’t get up again.
Cantigaster Venom kills permanently, even a drop of it is enough to cause the effects and the death it brings seems to be terribly painful. It can be coated on a blade or used to poison foods and drinks.
Chopping someone to pieces works terribly well, as the pieces possess no "life" of their own, and there is no chance to come back. The only exception is Feducci.
Cutting someone head off works well, but I suspect only because the head was lost in the struggle.
I suspect it would be the digestion process to kill us if we were to be swallowed whole, but possibly Sunless Sea will answer to this biting question.
As per burning I again must confess my ignorance on the subject. I have saved scores of rubbery men and tomb colonists from strangely recurring fires in the Carnival but I do not possess any insights on such a fate.
I suspect the damage the fire can do, and we must not forget the smoke which possibly is just as deadly, can be enough to damage you body enough to put you on the Boat permanently. but I’m just speculating.
This is all I can think about right now, so I leave the podium to others.