Cognomen Namsai (Namsai 
, น้ำใส) , worldwide, is a rare last name. The surname Namsai is habitual in South-eastern Asia, particularly Thailand, where it is quite a rare surname, Myanmar, where it is a very rare surname, and Malaysia, where it is an extremely rare surname. Not in comparison with a country's population, this name is the most popular in Thailand, Myanmar, and the United States. Very seldom, Namsai is the forename as well as the last name.