The simple rule is don’t drink tap water in Vietnam, with the exception of a few top hotels which now offer filtered water, and never drink river water. It’s wise also to avoid ice in your drinks except, again, in top hotels and other trustworthy places. Contaminated water is a major cause of sickness due to the presence of pathogenic organisms: bacteria, viruses and cysts. These micro-organisms cause ailments and diseases such as diarrhoea, gastroenteritis, typhoid, cholera, dysentery, poliomyelitis, hepatitis A and giardia – and can be present even when water looks clean and safe to drink.
Fortunately there are plenty of alternative drinks around: hot tea is always on offer, while cheap, bottled water and carbonated drinks are widely available. When buying bottled water check the seal is unbroken and the water is clear, as bottles are occasionally refilled from the tap. Tap water in Hanoi and Ho Chi Minh City is chlorinated and most travellers use it for brushing their teeth without problem, but this is not recommended in rural areas, where water is often untreated. Particular care should be taken anywhere where there is flooding as raw sewage may be washed into the water system.