演 ＝ 氵+ 寅 but what's it got to do with water!? How did it get its modern meanings? 氵+ 寅 = 演
zisea

拼音:yan3
①根据事理推广发挥：推～。讲～（亦作“演讲”）。～义（以史书及传说的材料为基础，增添一些细节，用章回体写成的小说）。～绎（一种推理方法，由一般原理推出关于特殊情况下的结论）。
②依照程式练习：～练。～示。～算。～武。～习。～兵场。
③不断变化：～变。～化。
④把技艺当众表现出来：表～。～出。～播。～奏。主～。义～。

I can't really see any reason water would be needed in this character from its above meanings.
Chinese Etymology

From water 氵水 and phonetic 寅. Original meaning to flow.
ShuoWen: (說文解字):
長流也一曰水名從水寅聲

If Chinese Etymology is not wrong - and I wouldn't be surprised if it is wrong - then how did it go from meaning water to what it means today?
http://dict.shufaji.com/word-2326.html

甲骨文（水，喻流程）（矢，代军事操练），造字本义：古代军事模拟实战的流程式操练。篆文将甲骨文的“矢”写成“寅”，明确了军事操练的含义。隶书将篆文的成。

the 氵also got another meaning of flow (process flow), so it does mean that process flor for traditional battle(war) training.