How is impurity washed from a non-absorbent object like a vessel?

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Washing impurity from a non-absorbent body, such as a vessel, is achieved by passing water over it once for each washing (ghasla), regardless of whether a human performs the act or it happens naturally, such as by rainwater falling upon it or flowing water in a river passing over it. Each pass of the river current counts as one washing because intent is not considered, resembling pouring water without intent. If the object falls into a small amount of stagnant water, the water becomes impure and the object is not purified. If the object is placed in a large amount of water, the mere presence and passage of water over its parts counts as one washing. If the object is agitated or moved within the water so that new parts of the water flow over it, this counts as a second washing, similar to multiple passes of running water.