Literally "fire and water cannot coexist"; used to describe two people or groups who are mutually exclusive or fundamentally opposed.

Describes two sides that are sharply opposed and cannot coexist, just like water and fire

(idiom) describes the relentless and destructive nature of fire and water disasters

in a state like water and fire; used to describe a situation where two parties are completely incompatible, intensely hostile, or at daggers drawn

to have no contact with others; to be completely out of touch with neighbors or society

(idiom) to have absolutely no dealings or relationship with one another; to be completely unrelated