From Tang poet Gao Shi's 《封丘作》: 世事尽付东流水 — 'worldly affairs all entrusted to the eastward flow'. China's major rivers flow east into the sea, making east-flowing water a natural metaphor for irreversible loss.
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Literal: 'hand it over to the east-flowing water'. Think of throwing something into a river and watching it disappear downstream.
