I am a pilot and work for an airline that subcontracts to a major airline and operates regional jets in the livery of the major airline. Regional airlines are not exactly renowned for high levels of service, or for their commitment to spending money on the little things that would be easy to scrimp on. From time to time, we are made aware of an aircraft that has been found to have an unacceptable level of bacteria contamination in the potable water tank that is used to supply water to the coffee makers and the sink in the lavatory. This is discovered in routine testing of the water quality and the offending water tank is not used until it has been treated and found to be within limits.
From this you can surmise that :
There is a water quality testing program in place.
Sometimes problems are found.
The problem is dealt with to prevent exposing passengers to contaminated water.
You can also assume that the testing and remediation is a scheduled maintenance program and does not detect contamination immediately when it happens. Therefore, a particular aircraft may operate normally, serving passengers normally with water from the tank which is unknowingly contaminated.
I see aircraft with the potable water tanks removed from service infrequently – perhaps once every couple of years. From this I surmise that it is a real problem, but relatively infrequent.
I drink the water that goes through the coffee maker. I know that it is very hot, in fact I can hear the water boiling on the heating element whenever I draw hot water out of the spigot. I assume that this is adequate to make it safe for consumption even if the water would be marginal, if tested. I would not ever drink water out of the cold tap in the lavatory. I use it to wash my hands, but consider that water very questionable.
I have colleagues that refuse to drink from the on board water supply whether it be coffee, tea or other. I understand their concerns but, as I show by my own choices, I consider their refusal to be an over reaction.
Water quality is one of those things that most people don’t think about very much, until it is a problem. It is one of those things that most people are better off not thinking about very much because if they knew all the details of the water they drink, it would bother them because virtually no water source is completely free of contamination.
An article about contamination of refillable water bottles:
The Gross Reason You Should Think Twice Before Drinking From Water Bottles
Author – George Stuart