You may drink from these water barrels without worries.
Lever: choose position 3 to unlock the secret door at 18. Depending on the lever's position the remaining secret doors will be unlocked.
A pirate is waiting on the watch platform.
Statue of Swafnir: donate a net or a trident by dropping it on location. Doing so deactivates the trap at 19 whereas the trap at 20 is activated. In case you do not donate anything, 19 is active and 20 is inactive.
This room contains various nautical items which are of no further interest to you
You should leave the boats alone. If the heroes ascend them, they will get lost in a maelstrom and are drowned (death-trap -> Game Over!)
Annotation: after successful battles against the pirates in the room with the statue of Swafnir and the adjoining room to the North, an iron key falls into your hands each time. These were thought to open the chests containing the sea chart and the praises probably. In Blade of Destiny, you may open the chests without them however.