This is the 2442nd most frequent Turkish word.
içen
"İçen" means "drinker" or "one who drinks."
Here, 'içen' is used as a relative clause to describe people who drink ('drinkers of') clean water.
Sadece temiz su içen insanlar daha sağlıklı olurlar.
People who only drink clean water are healthier.
'içenler' refers to 'those who drink; drinkers'; the suffix '-ler' pluralizes it.
Yemek yerken çay içenler daha fazla konuşur.
People who drink tea while eating talk more.
'içen' is used for 'the one who drinks,' referring to an individual habit.