יחזקאל, פרק ד׳, פסוק י״א

During times of siege, the most basic human needs become agonizing struggles. As part of a series of symbolic actions, the prophet is commanded to severely restrict his daily water intake. This harsh limitation serves as a vivid warning to the Israelites, illustrating the extreme distress and severe water shortage that will soon plague Jerusalem. Instead of drinking freely to satisfy their natural thirst, the people will be forced to carefully ration every drop [רד״ק, מצודת דוד].

The total daily allowance of water is restricted to a sixth of a hin, an amount estimated at roughly 750 milliliters [ביאור שטיינזלץ]. This small ration cannot be consumed all at once; rather, it must be carefully spread out over the course of the entire day [רש״י, מצודת דוד].

To fully capture the agony of this rationing, the prophet is instructed to drink using an exceptionally small measuring vessel [ביאור שטיינזלץ]. Clarifying the mechanics of this act, [רד״ק] explains that this tiny cup does not hold the full daily allowance. Instead, the prophet must use it to take minute sips from his daily ration. By drinking in such small, measured amounts, he is prevented from ever fully quenching his thirst at any given moment. This painful method of drinking physically demonstrates the deep deprivation and constant suffering that the residents of Jerusalem will endure throughout the long years of the siege.