"Running water is never stale and a door-hinge is never worm-eaten" means that constant motion prevents the inroads of germs and other organisms.

“流水不腐，户枢不蠹”，是说它们在不停的运动中抵抗了微生物或其他生物的侵蚀。

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Running water is never stale and a door-hinge never gets worm-eaten.

流水不腐，户枢不蠹。

《新英汉大辞典》