Originally Posted by
Eclipsepearl
No, there is NOT always a sign in the bathroom saying not to drink the water. On some flights, especially short hops, you might find them but on long-haul international, the water, in theory is drinkable.
A lack of a sign does not mean the water is not contaminated. Planes are filled up with water all over the world and getting bacteria out of the tanks is difficult.
Any contaminants in the water may not impact a healthy adult, but airplane water is not a good choice for those with compromised immune systems or for young children.
As for heating/boiling the water, water boils at a lower temperature at altitude so it does not get hot enough to kill bacteria.
As for filtered tank water, last I knew (which is when the studied were being done) Boeing only offered a filter for taste; there was no filter for bacteria.