Through Information we gathered through the Freedom of Information Act, we found fewer than half the airlines ordered as early as 2005 to begin testing their water have done so. Meantime, it's clear that some water on planes is contaminated.
It's something that happens on a routine basis at airports every day. Planes land and crews get that plane ready for the next flight. That includes filling the plane's holding tanks with fresh water.
Just how safe that fresh water is for you to drink may be reason for concern.
In 2004, tests conducted on 327 planes by the Environmental Protection Agency found 15-percent of the aircraft evaluated had water contaminated with coliform.
"Coliform bacteria can indicate that the water has been contaminated and it could be contaminated by something that can make people sick," explains June Weintraub, an epidemiologist with the San Francisco Department of Public Health.
The presence of coliform could mean other more harmful bacteria could be in the water, and that could lead to diarrhea, nausea and other symptoms.
Canada conducted its own tests on Canadian aircraft in 2006 and found similar results to the EPA.
This is the same water many airlines use to make your coffee and tea.
"For coffee and tea on an airplane, they don't boil it long enough to destroy any germs," says Weintraub.
It's also the same water you use to wash your hands or even brush your teeth on the plane. Weintraub says the bacteria can get on your hands and then be transmitted to your food.
We set out to examine just how much has improved since the EPA originally expressed concern in 2004.
"Airlines are doing a significant amount of monitoring, more monitoring and treating, flushing of their water systems," says Benjamin Grumbles with the EPA.
In fact, since 2005, 45 airlines have signed orders agreeing to test the water on those planes. But through the Freedom of Information Act, we discovered only 16 of those airlines have actually released results of those tests. Those tests results show water samples taken from 2,200 aircraft found coliform 10-percent of the time. Meantime, 29 airlines either haven't completed or begun their first round of testing or haven't released their test results.
We showed our findings to the senior scientist at the Natural Resources Defense Council in San Francisco and a member of the EPA's scientific advisory board on drinking water.
"We don't have data from some of the most major airlines out there. The data that we do have still shows contamination in quite a number of aircaft," says Gina Solomon with the Natural Resources Defense Council.
Delta, Continental, Northwest and United have released test results. However, American and US Airways are refusing to allow their data to be made public, claiming the results are "confidential business information."
That concerns Yeggie Dearborn, the laboratory director at Cel Analytical in San Francisco.
"I would probably not drink coffee anymore on the airline. I would probably just stick with canned sodas and stuff like that," says Dearborn.
Among the major airlines that have released data, 12-percent of the 323 planes tested by Delta over two years came back positive with coliform contaminated water. Delta says the overwhelming majority of its water samples came back negative.
Sampling on Continental revealed 16-percent of the 883 aircrafts tested found water contaminated with coliform. The airline believes that data is seriously inflated due to faulty testing procedures it is now working to improve.
Other averages include Northwest at 4-percent and United at 5.6-percent. United says it provides bottled water for brushing teeth and antiseptic napkins with every meal. Northwest says keeping its water supply free from contamination is a top priority.
According to the EPA, the tolerance for coliform in water is zero.
"We don't like to see any bacteria, especially coliform bacteria, in potable water, and especially not water that's being served to passengers," says Solomon.
A regional East Coast airline that served 12 million passengers in 2006 had the highest rate of positive tests for coliform -- 49-percent of the 84 aircraft tested by Atlantic Southeast contained water samples testing positive for coliform. The airline says if it detects coliform; it deactivates the water system until the problem is cleared.
Most passengers aren't aware there may be contaminated water on airplanes. However, Colin Finn of Foster City is the exception. He's concerned Air Canada is one of the few to serve tap water to customers requesting water on flights in the U.S. and Canada.
"On a trip we had just recently at Christmas time, traveled with my family, my kids all wanted to have water and I wouldn't let them have water," says Finn.
Air Canada says it serves tap water because it believes it is very clean and safe.
Information obtained through the Freedom of Information Act found several of the positive test results by United were conducted at San Francisco International Airport.
The San Francisco Public Utilities Commission conducts tests five days a week at the airport to make sure the water supply is not contaminated. The airport says the water it supplies the airlines is clean. In 2007, the airport found only one coliform reading out of 786 samples collected. They think the problem could be in the water tanks on the planes themselves.
"I have no idea if the tank was clean before they filled it up. Was it empty? Was it contaminated before they filled the water?" says San Francisco International Airport spokesperson, Mike McCarron.
San Jose Mineta International Airport reports it only had one test come back positive for coliform in 2007. Oakland International says all its water met federal and state drinking water standards.
However, water at the airport is just one source of potential contamination. Other possible sources include the water hose, the holding tanks and the plane's water system. All are maintained by each individual airline.
"If they're not cleaned properly, they could develop films of bacteria in them," says Dearborn.
The EPA hopes to release its proposal for safe drinking water on airlines within a few months.
"It will embrace treatment and monitoring and regular flushing. The EPA is pleased the airlines are working with us," says Grumbles.
Those airlines that don't comply could have their planes grounded. The Air Transport Association says the industry is working hard to insure water quality on board planes.
Ron Wilson is ABC7's aviation consultant. He thinks passengers need to be better informed about when airlines test their water and what those results might be.
"What you need on board an airplane in every restroom is a little placard on the wall that when they do the testing, they sign off on it and they tell you that the water is clean," says Wilson.
We've compiled all the data we've obtained through the Freedom of Information Act, including test results from each airline and a list of the airlines that have not yet completed or even begun testing. View the data below.