The Continuing Fear Of Bad Plane Water
The horror stories continue: "flight attendants will never drink tea or coffee on board because it's made from water believed to be frequently contaminated."
Coffee and tea are made with water stored in on-board tanks, not water brought aboard at each stop in plastic bottles.
The on-board tanks are the responsibility of the airline. They can be topped up as needed at any airport, although the airlines try to refill the water tanks at the aircraft's home airport in order to save mony.
The tanks are generally emptied completely only when the water system is being serviced or during periods when the aircraft will sit idle in cold weather.
These horror stories about on-board water tanks seem to go back to the early 2000s. A 2017 Travel and Leisure article was based on a Business Insider article, which quoted The Association of Flight Attendants - CWA as saying that they had pushed for a U.S. regulation "over 15 years ago", meaning in 2002 or earlier.
Some airline models have had on-board lavatories and sinks for some time. Below is the starboard lavatory from a Douglas DC-7 at the Smithsonian's National Air and Space Museum in Washington D.C. The DC-7 was the last major piston-engined transport aircraft made by the Douglas Corporation. 348 were built from 1953 to 1958.
In 2004 the U.S. Environmental Projection Agency sampled the water in 158 airliners. On 20 planes they found coliform bacteria, and on 2 planes that coliform bacteria included Escherichia coli, which is almost always the result of fecal contamination.
Drinking water in the U.S. is regulated under the Safe Drinking Water Act or SFWA, which was established by the EPA in 1974 and revised in 1986 and 1996. The EPA also developed the National Primary Drinking Water Regulations or NPDWR. It contains mandatory water quality standards for public water systems, limiting disinfectants and their by-products, inorganic and organic chemicals, radionuclide, and microorganisms.
The regulation calls for "routine disinfection and flushing" of the water system, and "periodic sampling". However, it's all based on self-inspection and following the aircraft manufacturer's recommendations. Obviously a manufacturer isn't going to say "Our planes have pretty dirty water tanks, you'd better check them frequently."
The regulation only requires that the air carrier inspect the on-board water system at least every five years and then resolve any problem within the following 90 days.
Health Canada conducted a similar study in 2006. They collected 431 water samples and found that 15.1% of the aircraft tested positive for total coliform bacteria, and 1.2% for E. coli.
Health Canada issued a warning to air travelers telling those with compromised immune systems to avoid beverages prepared from on-board tap water.
The existance of the EPA bothers some people.
Ayn Rand, Rand Paul, and Paul Ryan walk into the Objectivist Bar.
It's in an ideal Objectivist society, so there are no regulations.
The bartender serves them wood alcohol and everyone dies.
The Air Transport Association responded to the EPA report expressing skepticism over the statistical meaning of a sample of just 1% of the world-wide fleet. They especially objected to the EPA sampling procedures, as they had used was samples collected from the taps in the lavatories.
Given the tiny space and violent flushing, it would a surprise if fecal bacteria weren't found on all surfaces in an airliner lavatory!
A 2015 article in the International Journal of Environmental Research and Public Health went into deeper detail, and in 2017 they published an update in PLOS One. They took a total of 154 water samples. Perhaps most significantly, they took samples in the fore and aft galleys but not in the lavatories.
They concluded that the bacteria are usually introduced in the vehicles that transport water to the planes. The bacteria isn't in the original source, it is transferred from the truck to the plane.
They found a 200-fold increase in bacterial count going from the water source to the water service vehicle! (counted as the number of colony-forming units per volume of water). The water service vehicles vary widely, but in general they are much more contaminated than the water sources. The on-board water supply tanks are then conducive for further growth of the microorganisms introduced by the service vehicle.
The Good News
The (Hopefully Obvious) Warning
Do not drink water from the taps in the lavatory!
The high-speed vacuum flush, low ambient air pressure, and tight quarters coat the lavatory interior with a thin film of moisture from the toilet.