How is the quality of tap water in Thailand?

Question

Could you please advise on the quality of tap water in Thailand? Some people say it is only not suitable for drinking. And some people say it should not even be used for raising vegetables. I wonder if it is true, do local businesses really buy purified water to prepare food? I just do not want to like being overcautious while the food that I will eventually eat in a restaurant is prepared with lower measurements.

Also, when they say the water is not good, how is it polluted and what kind of pathogens is there? How a country with such a high level of rainfall is not able to supply drinkable water?

Answer 1

As a rule of thumb, tap water quality is poor but not terrible. Locals typically at least boil it before consumption, and any water you are served in a restaurant will be nam tom (น้ำต้ม), "boiled water". For what it's worth, I lived in central Bangkok on and off for over a year, eating quite a bit of street food and boiling the tap water for my own use, and never had any problems. As a short-term visitor it's still advisable to stick to 100% bottled/filtered water.

As for why, it's the typical situation in developing countries: the water coming out the purification plant is totally fine, but the quality of piping that moves it around is highly variable. That heavy rainfall actually makes things worse, since when the streets flood the odds of some of that dirty water making its way into cracks in the clean water pipes increases.

Answer 2

Officially in Thailand, although water quality likely is lower in rural areas, in urban areas like Bangkok, the water has met WHO standards for drinking for at least a decade:

In Bangkok, the Metropolitan Waterworks Authority (MWA) is responsible for the public water supply. The quality of its tap water meets World Health Organization (WHO) criteria and standards for drinking water and is safe to drink in all serviced areas (Metropolitan Waterworks Authority 2010).

In practice, however, as it is in many cities around the world, this water quality measure is only when the water leaves the water treatment plant. By the time the water makes it to the tap through kilometers of pipe of varying age and condition, it almost certainly will not be as clean.

Naturally, old cities, old neighborhoods, and old buildings can have old pipes. Old pipes can leak and rust as well as accumulate scale and sediment from the water itself. This can make the water less clean than it was when it left the water treatment plant.

In terms of specifics, the MWA displays the real-time water quality in each district in Thai in a chart and on a map on their website. If there were a particular issue with water quality or pathogens — after a flood, for example — it would be displayed accordingly.

Anecdotally, based on years of bouncing in and out of Bangkok, the local attitude generally is that tap water is acceptable for cooking, showering, and brushing your teeth, but not to drink. This observation vibes with a recent academic study, which found about half of locals in Bangkok view tap water as suitable to drink but far fewer actually drink it:

There was a significant prevalence (51.87%) of the acceptance of drinkable tap water among Bangkok residents. Among them, 82.99% selected tap water to drink and 9.79% drank water directly from the tap.

As a foreigner visiting Thailand, though, it is best to always stick to bottled water. Because locals tend to be very particular about taste, restaurants often do use some degree of water filtering in the prep process and tend to buy commercially prepared ice, but it should not be assumed.

A good rule of thumb when traveling is that because your personal intestinal flora may not be in sync with the water in any given location, it is best to limit your interaction with tap water.