Funny story there... It wasn't the primary loop, but it was off a secondary system- right by the chemical injection for a corrosion inhibitor called Morpholine. This was on another Nimitz-class, but during a shipyard availability, somebody swapped the pot water line for the coffee pot in the plant to the secondary feedwater side.
Now, Morpholine will give you THE WORST case of diarrhea you could imagine within about 20 minutes of ingesting it. It took the folks a couple of weeks to figure out why everybody was having the worst case of the runs ever, about 20 minutes after they would take the watch, or hold quarters, before they figured out that it was because of the crossed pot water lines.