How do I get the water element?
Solution 1:
The hint is: There is something underwater you must attach to your sub.
Spoiler answer:
In the upper left corner of the underwater area, there is a creature with a tentacle-esque appendage that can be attached to your submarine. Once the tentacle is attached, float down to the crab, remove the tentacle and attach it to said crab. Voila. The element is yours.