Compared to the previous one which is bad enough, this got to be a below-kindergartener level idiocy, lack of competent workers, or lack of concentration due to overwork, or all of the above.
From TEPCO's alerts for the press (here and here) and Jiji Tsushin (10/9/2013):
A worker of an affiliate company mistakenly removed the joint of the pipe that goes into the Reverse Osmosis Apparatus (line-3) at 10:01AM on October 9, 2013;
Amount of water leaked: 60 meters x 12 meters x several centimeters;
The leak was stopped 50 minutes later;
The leak is contained inside the temporary building that houses Reverse Osmosis Apparatus;
The leaked water had already been treated by SARRY (cesium absorption) but not yet by Reverse Osmosis Apparatus (desalination), meaning it is extremely high in beta nuclides (37 million Bq/L or 37,000 Bq/cm3);
The worker may have been splashed with this contaminated water with extremely high beta.