During the flight, tourists often notice that they are served cloudy water or cloudy tea. According to a flight attendant on Reddit, it’s quite common and often prompts passengers to ask, “Is this safe to drink?”
The expert explained that the water in the plane can appear cloudy because it comes from the water tank. “Everyone is asking about the water and whether it is safe to drink. To clarify, the tanks are cleaned regularly, but it depends on what you mean by “regular”. Ours work for a maximum of a week before they are cleaned. This is basic hygiene and safety. Filters are also built into our boilers before pouring tea or coffee. I have seen how people do not want to drink water because it seems cloudy. But this turbidity is not related to water, but air pressure. If you tap the side of the bottle or cup, the bubbles will disperse quickly,” she explained.
According to a water treatment worker who left a comment on the thread, the cloudy appearance of water and tea is mainly due to the mixture of oxygen and nitrogen in the water: “Water at ground level dissolves about 10 parts per million of oxygen and some nitrogen from the air. During the flight the plane, water begins to heat up, especially when it is poured into glasses for drinking. As the water gets warmer and also stirred, the dissolved oxygen comes out of the solution and makes the water cloudy. If you leave the water for a while, the oxygen bubbles will coalesce and the water will become clear, with some bubbles visible on the side of the glass.”
Mainly, tap water on flights is used for preparing hot drinks, and cold or drinking water at room temperature is served in bottles. Hygiene is crucial on board an aircraft and airlines have to follow strict rules about how often water systems are disinfected. So, after the coronavirus pandemic, many airlines have strengthened the on-board collection procedure.
Earlier, a 2019 scientific study suggested that passengers should avoid drinking tap water on airplanes because airplane water is often found to contain harmful bacteria. According to the observation of scientists, air carriers are required to disinfect and wash each water tank in the plane four times a year. This does not apply to airlines, which prefer to check their tanks every month – for them, disinfection and washing of tanks are mandatory only once a year.