What is the white tank between the right fender and inner fender for?
 

My son lost the right inner fender on his car and now I see a white tank. It is empty I know the one on the left side (drivers side) is for window washing fluid. What does this one do?

It passes to the engine compartment through a black rubber gromment but appears to be open. In other words, the white plastic tank has a neck that presses up against the black rubber but doesn/t extend pass it.

When I look from the engine side it looks like a oval cut out with nothing covering the opening.

Does the car still has the stock air box? If so, it is part of that system.

I guess that it catches the water that get sucked into the intake system
 

and then it sets there until it evaporates?

its to cancel out the resonance (sound) of the air intake.