Water 氵 beside 曷 — a phonetic that also asks 'when?'. Thirst is the body asking when water is coming. The same right side builds 喝 'to drink' with a mouth instead: thirst and drinking are one character-family, separated by a radical.
渴 powers one of the great strategy idioms: 望梅止渴 'quench thirst by picturing plums' — Cao Cao told his parched army an orchard lay ahead, and their mouths watered enough to march on. Motivation by imagination, 1800 years before sports psychology.
Asking 曷 'when's the water 氵 coming?' — THIRSTY.
渴望 'thirst-gaze' means to yearn — Chinese treats longing as a kind of thirst, which every bubble-tea queue confirms.