Is there drinking water at Ho Chi Minh City airport?

Yes, there is. Drinking water fountains are available at least in the baggage claim area and in the boarding area in both terminals. For more details on everything you need to know about Ho Chi Minh City airport, read here - https://nashaplaneta.net/asia/vietnam/saigon-hochimin-airport

How much does a visa to Vietnam cost?
Where to go in Vietnam for the first time?
Where is best to buy tours to Vietnam?
Follow the link, all these questions are discussed in the chat - https://t.me/vietnam_travel_chat