There's no way of knowing if there is permanent damage. Suggest you remove the keyboard which should improve the internal drying. You don't say what model PowerBook you have. This site gives you instructions for removing the keyboard. http://www.ifixit.com/Browse/PowerBook. You could use a hair dryer to shorten the drying time. Just don't get it too close to the Mac. It may take several days for all the water to evaporate.
I did a quick Google search. Be fortunate it was water. Other posters cited coffee, soda and cat urine. Look at these links.
Mini Tutorial: Liquid Mishaps: Dealing with accidental beverage spills on your PowerBook/iBook; external keyboard http://reviews.cnet.com/8301-13727_7-10333581-263.html