Symbolism, Imagery, Allegory
We've got a novel about sailors in Lord Jim, which means that water and the sea are like characters in and of themselves. Marlow spends a fair amount of time pondering the sea and its moods, personifying the sea like any sailor worth his salt should. And the sea brings about Jim's defining moment aboard the Patna.
One of the earliest passages we get describing the sea makes it sound downright monstrous:
And under the sinister splendor of that sky the sea, blue and profound, remained still, without a stir, without a ripple, without a wrinkle – viscous, stagnant, dead. (2.13)
Anything that "still" and "dead" just has to come back to life, right? And indeed the sea does, with a vengeance. When the Patna starts to go down (or at least appears to), water becomes a deadly force to be reckoned with, full of motion:
It was too dark just then for them to see each other, and, moreover, they were blinded and half drowned with the rain. He told me it was like being swept by a flood through a cavern. [...] The sea hissed "like twenty thousand kettles." (10.1)
Still, no matter how lethal the sea gets, we can't forget that water is also lifegiving in Lord Jim. As Jim freaks out aboard the Patna, one of the passengers begs him for water (at this point unaware that the ship is in any danger) reminding us that water is totally necessary for survival, even at sea, when sailors are surrounded by it. And when Jim gets a job as a water-clerk, it's all about helping ships get the supplies they need to survive at sea, including fresh drinking water. After all, sailors can't drink the sea; they can only sail atop it.
There are a lot of other instances of water and liquid being important in Lord Jim. Did you notice any? What about when Jim knocks over his drink while talking to Marlow (10.14)? Or the river that divides Patusan. What do you make of that?