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!