White water does have a knocker
but it only activates when you score a free game, not when you score an extra ball
THe knocker may have been removed or disabled (it maybe simply unplugged)
it is located in the upper left corner of the backbox
http://www.ipdb.org/showpic.pl?id=2768&picno=9358
Not true, mine always knocks when I get an extra ball
