But it isn't of non-potable quality - it is, in fact, potable:
The EPA did some work on this and presented results in Jan 2005 - EPA Airline Water Supplies.
Had a quick look at your link and read this:
9. What should the traveling public do?
The traveling public may benefit from the information released by EPA when deciding how they use the water that comes from aircraft tanks. Passengers with suppressed immune systems or others concerned should request bottled or canned beverages while on the aircraft and refrain from drinking tea or coffee that does not use bottled water. While boiling water for one minute will remove pathogens from drinking water, the water used to prepare coffee and tea aboard a plane is not generally brought to a sufficiently high temperature to guarantee that pathogens are killed.
Were you using the link to convince us that onboard tap water is safe?
The study quotes nearly 20% of tested water to be contaminated!