There is boiled water supply in each Tibet train. The water will not be ready for drinking until the temperature is up to 100℃, but as it is hard to boil the water on high altitude place, so the Tibet train has created new water supply facility, which water will be fully boiled at 70℃, these measures guarantee passengers to have clean drinking water. And the Shanghai to Lhasa train has water purifying system, so water is drinkable even not full boiled.
The water tank is usually located between 2 cars, serving hot water 24 hours in a day. You will need to bring your own container for getting the water, but please be careful of the hot water as the train is moving. You may also contact the train attendants for hot water supply, they can bring it to you at 08:00-18:00 in a day. Tip: Hot water is also available at Sink Area on Tibet train for cleaning or washing something, but the hot water at sink area is usually undrinkable.
There is unlimited access to boiling water from a tap in the hall on all Tibet trains so instant noodles, instant oatmeal, tea and anything else that just requires hot water are good things to pack with you (you can also buy instant noodles on board).