Cognomen น้ำใส (Namsai 
, Waeasae , Namsaii ) , in the world, is a rare last name. The cognomen น้ำใส is characteristic of 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. In absolute terms, it is the most numerous in Thailand, Myanmar, and the United States. Very seldom, น้ำใส is the forename as well as the last name.