This idiom was a sentence excerpted from one masterpiece written by Su Shi (sū shì 苏轼),who estabished himself as a renowned poet in The Song Dynasty (sòng cháo 宋朝,960—1279 AD). However,poetry creating was not the only hobby of this talented guy,drinking and travel were also two of his favorites. More often than not,he enjoyed himself very much in the natural world,breathing the fresh air,smelling the aroma of plants around,so as to relax and recharge his exhausted heart.

One day,Su Shi and a group of friends were boating in the Yangtse Rive (cháng jiāng 长江) in the area named Red Cliff (chì bì 赤壁). Letting the boat drift with the running water,floating on the surface of the river,they were totally fascinated by the grand and fantastic landscape that they saw. The moon threw a handful of gentle lights on the rocks amid the torrents,the water was roaring--what a beautiful picture it was! Being strongly inspired by what he had saw,one poem jumped into Su's mind instantly,one sentence of which was"When the water subsides the rocks emerge”, describing the scene of the river,since the river level was rather low during winter when they boated, a great deal of huge stones and rocks all came out of the water.

Afterwards,the meaning of “When the water subsides the rocks emerge” had changed. Now,it is used to refer that all secrets may eventually come to light.

苏轼是宋朝著名的诗人。他除了写诗歌之外，也喜欢喝酒和外出游玩。在大自然的怀抱中，他呼吸新鲜的空气，放松自己疲劳的心。

一天， 苏东坡又和一群友人来到赤壁下的长江岸边，登上小舟，泛舟游玩。这时，只听见东流的江水发出潺潺的声响，在这样寂静的夜晚，显得特别清脆。一座座高大的山峰屹立在两岸，显得格外陡峭。那时正值冬季，江水下落，江水之下的很多石头都露了出来。这壮观美丽的景观让苏轼诗兴大发，他当即作诗一首，其中的一句便是“山高月小，水落石出”。

“水落石出”，本来是指冬的一种风景，但后人把这"水落石出"四字，用做真相最终被发现的意思。

水落石出 (shuǐ luò shí chū)
【翻译】When the water subsides the rocks emerge.
【释义】水落下去，水底的石头就露出来。比喻事情的真相完全显露出来。
【例句】尽管这个案子非常复杂，但是在警察们的努力下，终于水落石出了。
【近义词】真相大白、原形毕露
【反义词】匿影藏形、扑朔迷离