You can think of irrigate as leading water to a place that needs it and letting it run across the whole surface. Someone opens a way — a ditch, a pipe, a tube — and the water keeps flowing until everything it touches has been reached. The water does not arrive by itself, and one splash is never enough.
「irrigate」可以想成：有人開了一條路給水走，水就沿著那條路一直流過整個面。水溝、水管、細管子都是那條路。重點有兩個：一是水是被引過來的，不會自己到；二是水要持續流，流到整片都碰到為止。抓住這個畫面，田地和傷口就是同一件事的兩個場景。
From the word’s history
First attested around 1615, borrowed from Latin irrigatus, the perfect passive participle of irrigo, formed from ir- (in, into) plus rigare (to water, to wet) — literally to lead water into something.
一六一五年前後進入英文，借自拉丁文 irrigātus，是動詞 irrigō 的完成被動分詞；irrigō 由 ir-（往裡面）加 rigāre（引水、弄濕）組成，字面上就是「把水引進去」。這正好就是今天兩個用法共用的畫面。
Wiktionary entry for irrigate (kaikki:3f6f69a190036ae4:1195917363), supplied in this packet
登入就可以看每一支怎麼連回核心畫面。