hé shuǐ bù fàn jǐng shuǐ
比喻互不干犯。
鲁迅《从与说起》：“而另一方面周瘦鹃在自己编的内说各种副刊有各种副刊的特性，作河水不犯井水之论。”
河水不犯井水作谓语、宾语、定语；指界限分明。
keep as clear of somebody as river water and well water
