I was at the airport recently waiting for my flight when I noticed a truck with a big sign that read “Waste Water.” It had huge hoses that I just knew had to be sewer hoses on steroids. This got me thinking: How do airplanes manage their water and holding tanks?
What I found out about airplane waste water is fascinating from an RVer’s perspective and not too different from what we do… except for the discharge in the air.
Fresh water in
Fresh, potable water is supplied to the plane by water trucks or, in some instances, a water hookup to the airport facilities. Water is pumped into the fresh water tanks and then pressurized to deliver a continual supply. Pipes can have heat trace wiring to prevent the water lines from freezing.
Aircraft can have multiple fresh water tanks on board and the amount of water can vary from 189 gallons to 600 gallons, depending on the aircraft. While the water is considered potable, there are multiple areas of potential contamination and it is not advised to actually drink it. Water that is used for cooking or drinking on board is bottled, distilled or filtered.
Gray water out
In the not-too-distant past, both gray water and black water were discharged in the air over oceans, countryside and even urban areas. No longer – at least the black water.
Gray water is usually discharged into the air where it (hopefully) evaporates. There is a check valve to prevent the plane from depressurization when the gray water is released and a heating element to prevent the waste water from freezing. If it is not discharged in flight, it becomes a big puddle on the tarmac under the plane.
Black water out
Most airline toilets now use a vacuum system that needs very little water to flush. The water used is mainly to “clean” the toilet bowl. That cuts down on the volume and weight in the black tank. Waste is delivered to the equivalent of an RV black water tank.
The older, recirculating toilets, while still on some airlines, are being replaced by the vacuum systems due to water weight and maintenance of the recirculating systems. The recirculating toilets flushed with water containing a blue dye, similar to the product used in portable toilets. The waste would then go through a macerator before being discharged.
Bring in the “honey wagon” for the airplane waste water
Here is where my curiosity began – the waste water trucks. The trucks are low profile to fit under the plane fuselage and use mammoth hoses to collect the waste. The workers in the truck I saw were wearing what looked like hazmat suits. A pair of latex gloves was just not going to cut it!
Related:
Dumping RV tanks: Where do you go when you gotta go?
##RVT1011
Years ago I was a ramper at DFW airport for a summer. First we drove a tug & trailer to the aircraft to fill the potable water tank. Afterwards, we drove a tug and a sewage discharge trailer beside the aircraft (747’s got an F-350 tanker) open the doors, check for leaks and attach the drain hose connector, check again, and open the valve. It works very much like an RV except no separate gray water tank. close the valve, wait a bit, disconnect the hose connection, and close the door. Some aircraft had two or more discharge tanks. If you ever need help emptying the tanks on your RV, just ask for help.
“In the not-too-distant past, both gray water and black water were discharged in the air over oceans, countryside and even urban areas. No longer – at least the black water.”
Maybe in some countries but not the USA. These aren’t cruise ships.
I began working in aviation in the early 70’s and our jets had no provisions to dump anywhere but on the ground into a honey truck. There wasn’t even any way to do it from inside. You had to manually open valves in an outside panel.
Gray and black were mixed together. The fresh tank was the same size as the wastewater tank.
When someone finds “blue ice” on the ground it’s because of a leaking system, not an intentional dump. https://en.wikipedia.org/wiki/Blue_ice_(aviation)
Years ago (around 1990) we took a crosscountry trip on Amtrak. When flushing after using the head, I was shocked to see the train track below! In 1976, we sat by the train tracks to watch the bi-centennial fireworks at historic Pearson Airpark. In 1992 there was a local news story about some track workers getting hit by you-know-what in the same area. Amtrak agreed to close the restrooms when approaching populated areas. I never thought about airliners doing the same thing. Ugh!!!
They don’t.
A young Airman was rousted from his warm bed at 2 AM at Keflavik Air Base, Iceland. Seems the pilot was not happy that the holding tanks of his C-141 had not been emptied to his liking. The Airman was not a happy camper and showed it as he shuffled about his duties with frozen effluent from the tank preventing a solid hose seal resulting in much of the waste dripping onto the tarmac and splashing the Airman.
The pilot, noticing that the Airman was not exhibiting the proper espirit d’ corps told him that he was going to report him to his superiors…to which the Airman replied, “Sir, it’s 0200, -25 degrees and I’ve got crap spilling onto my coveralls and down my sleeves. Just exactly what punishment do you think my superior is going to dish out that’s worse than this?”
Airliner holding tanks haven’t been able to dump in the air since the 50’s if even then.
It’s -40 degrees where we fly.
Also a good reason not to follow cattle trucks too close.
Keep your fingers crossed if one passes you…..we got a ‘gift’ one time.
Um, no the grey water isn’t sent overboard. We have a venting system and a few drops might be discharged, but otherwise it’s the same as an RV with the exception that everything is considered black water when it’s dumped.
Nanci… please give us your source of information indicating planes dispose of gray water over the oceans or rural areas…”Gray water is usually discharged into the air…” . I don’t believe this to be true TODAY one single bit…
Hello John, Happy to supply the source. Here is a link to the Engineering 360 newsletter. https://insights.globalspec.com/article/16509/airplane-water-and-wastewater-systems
The article you referenced was not very informed.
Back in the early years of passenger airplanes and rail roads there wasn’t holding tanks so everything went out when you flushed. Farmers loved the free fertilizer unless he was in the field at the time. I remember 70+ years ago riding the Illinois Central Rail Road signs were in each restroom “Please Do Not Flush While In The Station”. It went straight out in between the tracks. Of course back then many people in rural areas were still using out houses so nobody gave it much thought.
I’m a toy train collector (American Flyer post war 1946-1960). I also collect railroad memorabilia such as signs lanterns, photos, and etc. I have 2 signs that were in the bathrooms saying not to flush in the station, 1 Southern and the other Pennsylvania railroad’s. Just think of the person that followed someone after being in the station, the porter was responsible to make sure all toilets were empty after leaving the rail yards and on the open rail.