水掛け論

A fruitless argument is called mizukake ron in Japanese. It translates literally as "water-throwing argument," and the expression is said to have derived from a fight over water. Farmers cannot survive without water. In the old days before the introduction of proper irrigation systems, fights over water broke out frequently during periods of drought.

And it appears that the belligerents in those fights were not always total strangers. In a kyogen comic play titled "Mizukake Muko" (Water-throwing son-in-law), a man and his son-in-law fight over water for rice paddies. They start off by smearing each other's faces with mud. Water was so precious back then as to even ruin family relations.

みずかけ-ろん　みづ― ₄ 【水掛(け)論】

互いに自分の主張にこだわって論旨がかみあわず、際限なく続く議論。
「言った、言わないの―に終始する」

みずかけろん　水掛け論

a fruitless argument; an idle [a futile] discussion.