Sometimes water on the Intake
itself isn't enough. It all depends on how often it was cleaned. I would use a good aluminum/metal polish on it, using straight strokes rather than circular like on a window (get your minds out of the gutter). If that doesn't work, you will need to buff and polish it with a hand tool (straight strokes). On the filter don't use just water, use a cleaner specific to your filter. Just water won't do anything. Then follow the directions for the cleaner. Like said before, always clean the filter from the inside out and let dry at least overnight. If this is off the car like you said, it should be no problem cleaning everything like new. Do it now right before you install it.