The compound adjective 'well-watered' is a transparent formation from native English elements. The adverb 'well', with its ancient Proto-Germanic root wel meaning 'wish, good', combines with the verb 'water', descended from the essential Proto-Indo-European noun wódr̥. The '-ed' suffix, a common Germanic participial marker, completes the form. Literally describing land that has been abundantly supplied with water—a critical condition for fertility in agriculture—the term's logic is directly physical. This concrete meaning naturally extended into a common figurative sense, used to describe anything (like an economy or institution) that is amply supplied with the necessary resources for prosperity and growth, mirroring the vitality of irrigated soil.

Structure: well (adequately) + water (to supply with water) + ed (adjective suffix) - well: From Old English wel, meaning 'in a good way, suitably, abundantly'. It functions as an adverb modifying the verb 'water'. - water: From Old English wæter, meaning 'water'. In this compound, it functions as the verb stem meaning 'to supply with water'. - ed: From Old English -od, -ad, a suffix forming past participles of weak verbs, which here creates an adjective meaning 'having been watered'.