Water??? you can make matters only worse with water or a lubricant ...

If there is actually a debris inside the door cavity, you would need to remove that debris... start out with a powerful, commercial or industrial vacuum to see if you can suck anything from the door cavity through the window slit... chances are - you would not be able to do so... In this case, you would need to pull the door trim and use the same vacuum on the glass guides - first you need to check to see if the grinding noise is not coming from key parts broken... the main culprit in the windows' lifters is the plastic clip, that can crumble over time... once you get the issue of the debris out, you can use some lubricants... WD-40 is not a lubricant, it is a water displacer... silicon spray may work, also, you may consider graphite lubricants, they dry up in a dry kind of a surface and do not "leak" or "bleed" onto surrounding areas - so you don't end up with the glass edges being always greasy from the lubricant...