The Bangkok Metropolitan Waterworks Authority claims that the tap water in Bangkok is safe to drink and meets the standards set by the World Heal Organization and even though the locals do not recommended drinking tap water I’ve drunk it on occasion and have never gotten sick from it. However with the abundance of inexpensive bottled water options there is no reason to risk illness by drinking the tap water.
The easiest place to buy bottled water is from any local 7-11 convenience store. A large 6L (1.5 Gallon) bottle costs around 40 Baht ($1.25). The downside to buying these large bottles is having to carry them back to your home.
Many apartment buildings in Bangkok will have an onsite water filtration system. They are very inexpensive and a 6L bottle can be filled for around 10 – 15 Baht. Some high end luxury apartments and hotels will have a built in filtration system and they will usually have a small card by the sink letting you know if it’s safe to drink the water.
Another popular option of many Bangkok residents is to use a water delivery service such as Sprinkle Drinking Water. Sprinkle offers a number of different packages depending on your water consumption needs. Many of my friends use Sprinkle and I’ve only heard good things about their delivery service.