From Latin 'irrigare' (to water), from 'rigare' (to wet) — supplying water to land for agriculture.
To supply water to land or crops by means of channels, pipes, or streams to assist growth. In medicine, to flush a wound or body cavity with a continuous flow of water or solution.
From Latin irrigātus, the perfect passive participle of irrigāre (to water, to flood, to conduct water to land), composed of in- (into, upon, toward) and rigāre (to wet, to moisten, to conduct water). The verb rigāre has no certain IE etymology and may descend from a pre-Latin Mediterranean substrate word, though some link it tentatively to PIE *h₃reig- (moist, to reach). The prefix in- here is directional (into/onto) rather than negative — irrigāre is to direct water onto something. The Latin verb entered English legal
The earliest known irrigation systems date to around 6000 BCE in Mesopotamia and Egypt, but the Latin word 'irrigāre' may preserve an even older layer of language. Some linguists suspect that 'rigāre' (to wet) is not Indo-European at all but borrowed from a pre-Indo-European Mediterranean substrate language — the language of people who were farming and irrigating the land before the Indo-European speakers arrived. If so, the word itself may be as old as the technology it describes